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 $188.29   7.564%   $202.5323   $202.53   $202.55   $202.50  
  Purchase #2 $113.42   9.325%   $123.9964   $124.00   $124.00   $124.00  
  Purchase #3 $115.51   5.395%   $121.7418   $121.74   $121.75   $121.70  
  Purchase #4 $41.29   3.823%   $42.8685   $42.87   $42.85   $42.90  
  Purchase #5 $212.66   11.721%   $237.5859   $237.59   $237.60   $237.60  
  Purchase #6 $241.31   3.808%   $250.4991   $250.50   $250.50   $250.50  
  Purchase #7 $199.66   4.667%   $208.9781   $208.98   $209.00   $209.00  
  7 purchase totals = $1,112.14       $1,188.2021   $1,188.21   $1,188.25   $1,188.20