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 $144.87   7.463%   $155.6816   $155.68   $155.70   $155.70  
  Purchase #2 $59.78   4.726%   $62.6052   $62.61   $62.60   $62.60  
  Purchase #3 $19.45   6.763%   $20.7654   $20.77   $20.75   $20.80  
  Purchase #4 $17.57   11.577%   $19.6041   $19.60   $19.60   $19.60  
  Purchase #5 $235.67   6.635%   $251.3067   $251.31   $251.30   $251.30  
  Purchase #6 $247.95   7.674%   $266.9777   $266.98   $267.00   $267.00  
  Purchase #7 $187.76   3.138%   $193.6519   $193.65   $193.65   $193.70  
  7 purchase totals = $913.05       $970.5926   $970.60   $970.60   $970.70