Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $196.53   7.861%   $211.9792   $211.98   $212.00   $212.00  
  Purchase #2 $108.66   4.280%   $113.3106   $113.31   $113.30   $113.30  
  Purchase #3 $155.43   7.107%   $166.4764   $166.48   $166.50   $166.50  
  Purchase #4 $197.95   11.283%   $220.2847   $220.28   $220.30   $220.30  
  Purchase #5 $167.36   3.730%   $173.6025   $173.60   $173.60   $173.60  
  Purchase #6 $172.30   10.516%   $190.4191   $190.42   $190.40   $190.40  
  Purchase #7 $167.39   11.579%   $186.7721   $186.77   $186.75   $186.80  
  7 purchase totals = $1,165.62       $1,262.8446   $1,262.84   $1,262.85   $1,262.90