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 $168.61   9.241%   $184.1913   $184.19   $184.20   $184.20  
  Purchase #2 $144.31   7.792%   $155.5546   $155.55   $155.55   $155.60  
  Purchase #3 $177.64   9.874%   $195.1802   $195.18   $195.20   $195.20  
  Purchase #4 $200.68   8.271%   $217.2782   $217.28   $217.30   $217.30  
  Purchase #5 $123.56   4.791%   $129.4798   $129.48   $129.50   $129.50  
  Purchase #6 $108.85   13.412%   $123.449   $123.45   $123.45   $123.40  
  Purchase #7 $136.73   5.437%   $144.164   $144.16   $144.15   $144.20  
  7 purchase totals = $1,060.38       $1,149.2971   $1,149.29   $1,149.35   $1,149.40