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 $87.45   10.113%   $96.2938   $96.29   $96.30   $96.30  
  Purchase #2 $198.73   13.245%   $225.0518   $225.05   $225.05   $225.10  
  Purchase #3 $178.98   6.740%   $191.0433   $191.04   $191.05   $191.00  
  Purchase #4 $43.77   8.355%   $47.427   $47.43   $47.45   $47.40  
  Purchase #5 $128.28   9.272%   $140.1741   $140.17   $140.15   $140.20  
  Purchase #6 $136.25   12.263%   $152.9583   $152.96   $152.95   $153.00  
  Purchase #7 $46.80   4.602%   $48.9537   $48.95   $48.95   $49.00  
  7 purchase totals = $820.26       $901.9020   $901.89   $901.90   $902.00