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 $225.33   9.546%   $246.84   $246.84   $246.85   $246.80  
  Purchase #2 $178.99   4.125%   $186.3733   $186.37   $186.35   $186.40  
  Purchase #3 $68.31   5.254%   $71.899   $71.90   $71.90   $71.90  
  Purchase #4 $169.78   8.560%   $184.3132   $184.31   $184.30   $184.30  
  Purchase #5 $243.68   9.474%   $266.7662   $266.77   $266.75   $266.80  
  Purchase #6 $219.83   11.609%   $245.3501   $245.35   $245.35   $245.40  
  Purchase #7 $103.27   13.337%   $117.0431   $117.04   $117.05   $117.00  
  7 purchase totals = $1,209.19       $1,318.5849   $1,318.58   $1,318.55   $1,318.60