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 $185.46   8.559%   $201.3335   $201.33   $201.35   $201.30  
  Purchase #2 $87.79   7.434%   $94.3163   $94.32   $94.30   $94.30  
  Purchase #3 $212.50   7.524%   $228.4885   $228.49   $228.50   $228.50  
  Purchase #4 $121.49   11.667%   $135.6642   $135.66   $135.65   $135.70  
  Purchase #5 $196.95   3.429%   $203.7034   $203.70   $203.70   $203.70  
  Purchase #6 $40.57   6.839%   $43.3446   $43.34   $43.35   $43.30  
  Purchase #7 $102.41   13.541%   $116.2773   $116.28   $116.30   $116.30  
  7 purchase totals = $947.17       $1,023.1278   $1,023.12   $1,023.15   $1,023.10