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 $233.27   11.434%   $259.9421   $259.94   $259.95   $259.90  
  Purchase #2 $36.68   5.739%   $38.7851   $38.79   $38.80   $38.80  
  Purchase #3 $159.73   4.306%   $166.608   $166.61   $166.60   $166.60  
  Purchase #4 $189.47   12.171%   $212.5304   $212.53   $212.55   $212.50  
  Purchase #5 $184.50   10.384%   $203.6585   $203.66   $203.65   $203.70  
  Purchase #6 $205.84   6.214%   $218.6309   $218.63   $218.65   $218.60  
  Purchase #7 $186.37   7.293%   $199.962   $199.96   $199.95   $200.00  
  7 purchase totals = $1,195.86       $1,300.1170   $1,300.12   $1,300.15   $1,300.10