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 $33.30   3.847%   $34.5811   $34.58   $34.60   $34.60  
  Purchase #2 $113.93   13.814%   $129.6683   $129.67   $129.65   $129.70  
  Purchase #3 $209.41   6.323%   $222.651   $222.65   $222.65   $222.70  
  Purchase #4 $122.53   6.317%   $130.2702   $130.27   $130.25   $130.30  
  Purchase #5 $219.75   6.378%   $233.7657   $233.77   $233.75   $233.80  
  Purchase #6 $139.33   5.504%   $146.9987   $147.00   $147.00   $147.00  
  Purchase #7 $57.69   8.734%   $62.7286   $62.73   $62.75   $62.70  
  7 purchase totals = $895.94       $960.6636   $960.67   $960.65   $960.80