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 $64.47   7.758%   $69.4716   $69.47   $69.45   $69.50  
  Purchase #2 $231.37   6.192%   $245.6964   $245.70   $245.70   $245.70  
  Purchase #3 $163.48   9.288%   $178.664   $178.66   $178.65   $178.70  
  Purchase #4 $158.59   11.280%   $176.479   $176.48   $176.50   $176.50  
  Purchase #5 $144.72   11.518%   $161.3888   $161.39   $161.40   $161.40  
  Purchase #6 $240.82   12.593%   $271.1465   $271.15   $271.15   $271.10  
  Purchase #7 $86.56   12.819%   $97.6561   $97.66   $97.65   $97.70  
  7 purchase totals = $1,090.01       $1,200.5024   $1,200.51   $1,200.50   $1,200.60