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 $88.26   5.544%   $93.1531   $93.15   $93.15   $93.20  
  Purchase #2 $193.27   6.355%   $205.5523   $205.55   $205.55   $205.60  
  Purchase #3 $40.52   12.569%   $45.613   $45.61   $45.60   $45.60  
  Purchase #4 $88.54   9.288%   $96.7636   $96.76   $96.75   $96.80  
  Purchase #5 $225.32   11.453%   $251.1259   $251.13   $251.15   $251.10  
  Purchase #6 $173.70   11.845%   $194.2748   $194.27   $194.25   $194.30  
  Purchase #7 $97.69   7.747%   $105.258   $105.26   $105.25   $105.30  
  7 purchase totals = $907.30       $991.7407   $991.73   $991.70   $991.90