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 $218.98   5.814%   $231.7115   $231.71   $231.70   $231.70  
  Purchase #2 $180.88   11.802%   $202.2275   $202.23   $202.25   $202.20  
  Purchase #3 $124.54   5.290%   $131.1282   $131.13   $131.15   $131.10  
  Purchase #4 $37.32   5.193%   $39.258   $39.26   $39.25   $39.30  
  Purchase #5 $167.79   3.290%   $173.3103   $173.31   $173.30   $173.30  
  Purchase #6 $25.34   3.795%   $26.3017   $26.30   $26.30   $26.30  
  Purchase #7 $128.45   13.112%   $145.2924   $145.29   $145.30   $145.30  
  7 purchase totals = $883.30       $949.2296   $949.23   $949.25   $949.20