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 $55.78   9.442%   $61.0467   $61.05   $61.05   $61.00  
  Purchase #2 $54.53   6.485%   $58.0663   $58.07   $58.05   $58.10  
  Purchase #3 $233.95   5.641%   $247.1471   $247.15   $247.15   $247.10  
  Purchase #4 $87.80   7.771%   $94.6229   $94.62   $94.60   $94.60  
  Purchase #5 $184.51   11.711%   $206.118   $206.12   $206.10   $206.10  
  Purchase #6 $149.46   6.545%   $159.2422   $159.24   $159.25   $159.20  
  Purchase #7 $172.64   12.839%   $194.8052   $194.81   $194.80   $194.80  
  7 purchase totals = $938.67       $1,021.0484   $1,021.06   $1,021.00   $1,020.90