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 $66.26   4.232%   $69.0641   $69.06   $69.05   $69.10  
  Purchase #2 $175.74   13.609%   $199.6565   $199.66   $199.65   $199.70  
  Purchase #3 $144.41   13.764%   $164.2866   $164.29   $164.30   $164.30  
  Purchase #4 $179.51   13.123%   $203.0671   $203.07   $203.05   $203.10  
  Purchase #5 $244.77   13.161%   $276.9842   $276.98   $277.00   $277.00  
  Purchase #6 $76.76   11.822%   $85.8346   $85.83   $85.85   $85.80  
  Purchase #7 $120.28   13.168%   $136.1185   $136.12   $136.10   $136.10  
  7 purchase totals = $1,007.73       $1,135.0116   $1,135.01   $1,135.00   $1,135.10