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 $41.77   11.438%   $46.5477   $46.55   $46.55   $46.50  
  Purchase #2 $93.70   3.757%   $97.2203   $97.22   $97.20   $97.20  
  Purchase #3 $181.45   8.386%   $196.6664   $196.67   $196.65   $196.70  
  Purchase #4 $219.73   6.793%   $234.6563   $234.66   $234.65   $234.70  
  Purchase #5 $88.40   12.464%   $99.4182   $99.42   $99.40   $99.40  
  Purchase #6 $55.37   10.562%   $61.2182   $61.22   $61.20   $61.20  
  Purchase #7 $223.31   3.252%   $230.572   $230.57   $230.55   $230.60  
  7 purchase totals = $903.73       $966.2991   $966.31   $966.20   $966.30