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 $66.49   10.554%   $73.5074   $73.51   $73.50   $73.50  
  Purchase #2 $226.65   3.736%   $235.1176   $235.12   $235.10   $235.10  
  Purchase #3 $147.65   10.588%   $163.2832   $163.28   $163.30   $163.30  
  Purchase #4 $95.75   11.671%   $106.925   $106.93   $106.95   $106.90  
  Purchase #5 $59.59   8.276%   $64.5217   $64.52   $64.50   $64.50  
  Purchase #6 $11.86   12.111%   $13.2964   $13.30   $13.30   $13.30  
  Purchase #7 $150.43   12.780%   $169.655   $169.66   $169.65   $169.70  
  7 purchase totals = $758.42       $826.3063   $826.32   $826.30   $826.30