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 $236.70   4.741%   $247.9219   $247.92   $247.90   $247.90  
  Purchase #2 $169.99   3.407%   $175.7816   $175.78   $175.80   $175.80  
  Purchase #3 $14.77   12.547%   $16.6232   $16.62   $16.60   $16.60  
  Purchase #4 $228.52   7.118%   $244.7861   $244.79   $244.80   $244.80  
  Purchase #5 $177.64   11.440%   $197.962   $197.96   $197.95   $198.00  
  Purchase #6 $20.56   3.151%   $21.2078   $21.21   $21.20   $21.20  
  Purchase #7 $58.93   9.614%   $64.5955   $64.60   $64.60   $64.60  
  7 purchase totals = $907.11       $968.8781   $968.88   $968.85   $968.90