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 $62.87   9.279%   $68.7037   $68.70   $68.70   $68.70  
  Purchase #2 $159.37   12.317%   $178.9996   $179.00   $179.00   $179.00  
  Purchase #3 $228.26   7.612%   $245.6352   $245.64   $245.65   $245.60  
  Purchase #4 $169.42   4.762%   $177.4878   $177.49   $177.50   $177.50  
  Purchase #5 $161.96   6.795%   $172.9652   $172.97   $172.95   $173.00  
  Purchase #6 $123.32   10.363%   $136.0997   $136.10   $136.10   $136.10  
  Purchase #7 $86.28   7.303%   $92.581   $92.58   $92.60   $92.60  
  7 purchase totals = $991.48       $1,072.4722   $1,072.48   $1,072.50   $1,072.50