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 $84.53   12.766%   $95.3211   $95.32   $95.30   $95.30  
  Purchase #2 $110.84   6.108%   $117.6101   $117.61   $117.60   $117.60  
  Purchase #3 $46.84   11.217%   $52.094   $52.09   $52.10   $52.10  
  Purchase #4 $125.28   9.785%   $137.5386   $137.54   $137.55   $137.50  
  Purchase #5 $240.43   11.200%   $267.3582   $267.36   $267.35   $267.40  
  Purchase #6 $71.63   12.822%   $80.8144   $80.81   $80.80   $80.80  
  Purchase #7 $190.94   8.592%   $207.3456   $207.35   $207.35   $207.30  
  7 purchase totals = $870.49       $958.0820   $958.08   $958.05   $958.00