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 $162.94   9.285%   $178.069   $178.07   $178.05   $178.10  
  Purchase #2 $134.66   11.321%   $149.9049   $149.90   $149.90   $149.90  
  Purchase #3 $182.65   11.460%   $203.5817   $203.58   $203.60   $203.60  
  Purchase #4 $83.87   9.669%   $91.9794   $91.98   $92.00   $92.00  
  Purchase #5 $141.71   5.506%   $149.5126   $149.51   $149.50   $149.50  
  Purchase #6 $216.26   6.250%   $229.7763   $229.78   $229.80   $229.80  
  Purchase #7 $234.79   11.788%   $262.467   $262.47   $262.45   $262.50  
  7 purchase totals = $1,156.88       $1,265.2909   $1,265.29   $1,265.30   $1,265.40