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 $201.29   13.269%   $227.9992   $228.00   $228.00   $228.00  
  Purchase #2 $145.27   5.770%   $153.6521   $153.65   $153.65   $153.70  
  Purchase #3 $35.60   6.242%   $37.8222   $37.82   $37.80   $37.80  
  Purchase #4 $113.75   6.543%   $121.1927   $121.19   $121.20   $121.20  
  Purchase #5 $89.93   13.712%   $102.2612   $102.26   $102.25   $102.30  
  Purchase #6 $59.86   7.200%   $64.1699   $64.17   $64.15   $64.20  
  Purchase #7 $31.98   4.814%   $33.5195   $33.52   $33.50   $33.50  
  7 purchase totals = $677.68       $740.6168   $740.61   $740.55   $740.70