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 $42.49   5.165%   $44.6846   $44.68   $44.70   $44.70  
  Purchase #2 $57.93   8.200%   $62.6803   $62.68   $62.70   $62.70  
  Purchase #3 $194.37   13.705%   $221.0084   $221.01   $221.00   $221.00  
  Purchase #4 $96.99   13.724%   $110.3009   $110.30   $110.30   $110.30  
  Purchase #5 $238.50   7.127%   $255.4979   $255.50   $255.50   $255.50  
  Purchase #6 $245.27   4.647%   $256.6677   $256.67   $256.65   $256.70  
  Purchase #7 $99.96   12.235%   $112.1901   $112.19   $112.20   $112.20  
  7 purchase totals = $975.51       $1,063.0299   $1,063.03   $1,063.05   $1,063.10