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 $180.95   12.453%   $203.4837   $203.48   $203.50   $203.50  
  Purchase #2 $200.72   13.246%   $227.3074   $227.31   $227.30   $227.30  
  Purchase #3 $190.98   13.614%   $216.98   $216.98   $217.00   $217.00  
  Purchase #4 $89.27   6.372%   $94.9583   $94.96   $94.95   $95.00  
  Purchase #5 $236.95   8.261%   $256.5244   $256.52   $256.50   $256.50  
  Purchase #6 $20.82   9.797%   $22.8597   $22.86   $22.85   $22.90  
  Purchase #7 $192.39   5.206%   $202.4058   $202.41   $202.40   $202.40  
  7 purchase totals = $1,112.08       $1,224.5193   $1,224.52   $1,224.50   $1,224.60