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 $60.47   5.592%   $63.8515   $63.85   $63.85   $63.90  
  Purchase #2 $224.41   8.698%   $243.9292   $243.93   $243.95   $243.90  
  Purchase #3 $63.50   10.536%   $70.1904   $70.19   $70.20   $70.20  
  Purchase #4 $104.62   3.510%   $108.2922   $108.29   $108.30   $108.30  
  Purchase #5 $177.25   9.701%   $194.445   $194.45   $194.45   $194.40  
  Purchase #6 $204.25   7.682%   $219.9405   $219.94   $219.95   $219.90  
  Purchase #7 $67.52   12.524%   $75.9762   $75.98   $76.00   $76.00  
  7 purchase totals = $902.02       $976.6250   $976.63   $976.70   $976.60