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 $193.75   5.237%   $203.8967   $203.90   $203.90   $203.90  
  Purchase #2 $110.58   5.204%   $116.3346   $116.33   $116.35   $116.30  
  Purchase #3 $14.56   10.350%   $16.067   $16.07   $16.05   $16.10  
  Purchase #4 $170.35   6.846%   $182.0122   $182.01   $182.00   $182.00  
  Purchase #5 $112.80   6.324%   $119.9335   $119.93   $119.95   $119.90  
  Purchase #6 $138.91   10.718%   $153.7984   $153.80   $153.80   $153.80  
  Purchase #7 $57.92   5.711%   $61.2278   $61.23   $61.25   $61.20  
  7 purchase totals = $798.87       $853.2702   $853.27   $853.30   $853.20