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 $221.62   7.385%   $237.9866   $237.99   $238.00   $238.00  
  Purchase #2 $106.26   9.717%   $116.5853   $116.59   $116.60   $116.60  
  Purchase #3 $28.41   9.644%   $31.1499   $31.15   $31.15   $31.10  
  Purchase #4 $148.45   12.840%   $167.511   $167.51   $167.50   $167.50  
  Purchase #5 $105.69   4.212%   $110.1417   $110.14   $110.15   $110.10  
  Purchase #6 $120.96   7.244%   $129.7223   $129.72   $129.70   $129.70  
  Purchase #7 $137.60   4.155%   $143.3173   $143.32   $143.30   $143.30  
  7 purchase totals = $868.99       $936.4141   $936.42   $936.40   $936.30