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 $84.62   10.273%   $93.313   $93.31   $93.30   $93.30  
  Purchase #2 $84.66   11.711%   $94.5745   $94.57   $94.55   $94.60  
  Purchase #3 $184.99   3.311%   $191.115   $191.12   $191.10   $191.10  
  Purchase #4 $215.57   10.302%   $237.778   $237.78   $237.80   $237.80  
  Purchase #5 $223.97   10.820%   $248.2036   $248.20   $248.20   $248.20  
  Purchase #6 $26.62   5.573%   $28.1035   $28.10   $28.10   $28.10  
  Purchase #7 $32.84   4.191%   $34.2163   $34.22   $34.20   $34.20  
  7 purchase totals = $853.27       $927.3039   $927.30   $927.25   $927.30