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 $54.31   3.485%   $56.2027   $56.20   $56.20   $56.20  
  Purchase #2 $237.52   7.208%   $254.6404   $254.64   $254.65   $254.60  
  Purchase #3 $120.47   13.793%   $137.0864   $137.09   $137.10   $137.10  
  Purchase #4 $125.51   5.569%   $132.4997   $132.50   $132.50   $132.50  
  Purchase #5 $212.43   8.615%   $230.7308   $230.73   $230.75   $230.70  
  Purchase #6 $163.95   12.706%   $184.7815   $184.78   $184.80   $184.80  
  Purchase #7 $240.81   11.106%   $267.5544   $267.55   $267.55   $267.60  
  7 purchase totals = $1,155.00       $1,263.4959   $1,263.49   $1,263.55   $1,263.50