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 $189.57   5.830%   $200.6219   $200.62   $200.60   $200.60  
  Purchase #2 $215.41   11.717%   $240.6496   $240.65   $240.65   $240.60  
  Purchase #3 $207.39   4.319%   $216.3472   $216.35   $216.35   $216.30  
  Purchase #4 $98.54   9.112%   $107.519   $107.52   $107.50   $107.50  
  Purchase #5 $60.95   5.531%   $64.3211   $64.32   $64.30   $64.30  
  Purchase #6 $36.79   11.194%   $40.9083   $40.91   $40.90   $40.90  
  Purchase #7 $49.60   12.527%   $55.8134   $55.81   $55.80   $55.80  
  7 purchase totals = $858.25       $926.1805   $926.18   $926.10   $926.00