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 $188.46   8.746%   $204.9427   $204.94   $204.95   $204.90  
  Purchase #2 $184.98   8.252%   $200.2445   $200.24   $200.25   $200.20  
  Purchase #3 $86.91   12.292%   $97.593   $97.59   $97.60   $97.60  
  Purchase #4 $204.77   11.823%   $228.98   $228.98   $229.00   $229.00  
  Purchase #5 $193.26   5.252%   $203.41   $203.41   $203.40   $203.40  
  Purchase #6 $6.75   7.281%   $7.2415   $7.24   $7.25   $7.20  
  Purchase #7 $91.82   4.519%   $95.9693   $95.97   $95.95   $96.00  
  7 purchase totals = $956.95       $1,038.3810   $1,038.37   $1,038.40   $1,038.30