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 $61.93   10.638%   $68.5181   $68.52   $68.50   $68.50  
  Purchase #2 $176.58   11.552%   $196.9785   $196.98   $197.00   $197.00  
  Purchase #3 $76.98   13.239%   $87.1714   $87.17   $87.15   $87.20  
  Purchase #4 $156.27   4.162%   $162.774   $162.77   $162.75   $162.80  
  Purchase #5 $87.41   4.570%   $91.4046   $91.40   $91.40   $91.40  
  Purchase #6 $173.67   4.666%   $181.7734   $181.77   $181.75   $181.80  
  Purchase #7 $101.57   6.181%   $107.848   $107.85   $107.85   $107.80  
  7 purchase totals = $834.41       $896.4680   $896.46   $896.40   $896.50