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 $48.67   9.408%   $53.2489   $53.25   $53.25   $53.20  
  Purchase #2 $127.60   13.263%   $144.5236   $144.52   $144.50   $144.50  
  Purchase #3 $115.56   12.162%   $129.6144   $129.61   $129.60   $129.60  
  Purchase #4 $153.50   11.219%   $170.7212   $170.72   $170.70   $170.70  
  Purchase #5 $150.28   13.720%   $170.8984   $170.90   $170.90   $170.90  
  Purchase #6 $198.40   3.127%   $204.604   $204.60   $204.60   $204.60  
  Purchase #7 $89.95   5.629%   $95.0133   $95.01   $95.00   $95.00  
  7 purchase totals = $883.96       $968.6238   $968.61   $968.55   $968.50