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 $87.64   8.620%   $95.1946   $95.19   $95.20   $95.20  
  Purchase #2 $80.81   4.121%   $84.1402   $84.14   $84.15   $84.10  
  Purchase #3 $106.55   6.156%   $113.1092   $113.11   $113.10   $113.10  
  Purchase #4 $63.55   13.132%   $71.8954   $71.90   $71.90   $71.90  
  Purchase #5 $197.85   12.575%   $222.7296   $222.73   $222.75   $222.70  
  Purchase #6 $104.84   5.289%   $110.385   $110.39   $110.40   $110.40  
  Purchase #7 $247.67   7.132%   $265.3338   $265.33   $265.35   $265.30  
  7 purchase totals = $888.91       $962.7878   $962.79   $962.85   $962.70