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 $184.69   12.578%   $207.9203   $207.92   $207.90   $207.90  
  Purchase #2 $36.51   6.271%   $38.7995   $38.80   $38.80   $38.80  
  Purchase #3 $141.25   13.140%   $159.8103   $159.81   $159.80   $159.80  
  Purchase #4 $247.34   11.423%   $275.5936   $275.59   $275.60   $275.60  
  Purchase #5 $160.59   3.444%   $166.1207   $166.12   $166.10   $166.10  
  Purchase #6 $238.72   9.123%   $260.4984   $260.50   $260.50   $260.50  
  Purchase #7 $137.83   12.598%   $155.1938   $155.19   $155.20   $155.20  
  7 purchase totals = $1,146.93       $1,263.9366   $1,263.93   $1,263.90   $1,263.90