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 $32.95   11.383%   $36.7007   $36.70   $36.70   $36.70  
  Purchase #2 $140.85   13.492%   $159.8535   $159.85   $159.85   $159.90  
  Purchase #3 $173.92   7.482%   $186.9327   $186.93   $186.95   $186.90  
  Purchase #4 $215.27   11.517%   $240.0626   $240.06   $240.05   $240.10  
  Purchase #5 $108.65   9.645%   $119.1293   $119.13   $119.15   $119.10  
  Purchase #6 $152.72   13.708%   $173.6549   $173.65   $173.65   $173.70  
  Purchase #7 $160.73   4.554%   $168.0496   $168.05   $168.05   $168.00  
  7 purchase totals = $985.09       $1,084.3833   $1,084.37   $1,084.40   $1,084.40