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 $83.97   8.754%   $91.3207   $91.32   $91.30   $91.30  
  Purchase #2 $229.67   3.331%   $237.3203   $237.32   $237.30   $237.30  
  Purchase #3 $15.49   7.315%   $16.6231   $16.62   $16.60   $16.60  
  Purchase #4 $43.44   13.644%   $49.367   $49.37   $49.35   $49.40  
  Purchase #5 $153.92   4.415%   $160.7156   $160.72   $160.70   $160.70  
  Purchase #6 $187.79   3.594%   $194.5392   $194.54   $194.55   $194.50  
  Purchase #7 $153.90   13.571%   $174.7858   $174.79   $174.80   $174.80  
  7 purchase totals = $868.18       $924.6717   $924.68   $924.60   $924.60