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 $56.28   11.696%   $62.8625   $62.86   $62.85   $62.90  
  Purchase #2 $112.90   9.585%   $123.7215   $123.72   $123.70   $123.70  
  Purchase #3 $180.74   6.612%   $192.6905   $192.69   $192.70   $192.70  
  Purchase #4 $25.78   13.571%   $29.2786   $29.28   $29.30   $29.30  
  Purchase #5 $29.85   7.121%   $31.9756   $31.98   $32.00   $32.00  
  Purchase #6 $230.55   13.137%   $260.8374   $260.84   $260.85   $260.80  
  Purchase #7 $154.74   13.433%   $175.5262   $175.53   $175.55   $175.50  
  7 purchase totals = $790.84       $876.8923   $876.90   $876.95   $876.90