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 $179.28   8.487%   $194.4955   $194.50   $194.50   $194.50  
  Purchase #2 $192.32   13.539%   $218.3582   $218.36   $218.35   $218.40  
  Purchase #3 $234.35   13.319%   $265.5631   $265.56   $265.55   $265.60  
  Purchase #4 $32.84   7.626%   $35.3444   $35.34   $35.35   $35.30  
  Purchase #5 $173.43   9.671%   $190.2024   $190.20   $190.20   $190.20  
  Purchase #6 $22.53   10.759%   $24.954   $24.95   $24.95   $25.00  
  Purchase #7 $118.51   11.305%   $131.9076   $131.91   $131.90   $131.90  
  7 purchase totals = $953.26       $1,060.8252   $1,060.82   $1,060.80   $1,060.90