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 $247.38   3.203%   $255.3036   $255.30   $255.30   $255.30  
  Purchase #2 $132.52   11.194%   $147.3543   $147.35   $147.35   $147.40  
  Purchase #3 $137.43   8.619%   $149.2751   $149.28   $149.30   $149.30  
  Purchase #4 $227.58   4.739%   $238.365   $238.37   $238.35   $238.40  
  Purchase #5 $218.40   5.397%   $230.187   $230.19   $230.20   $230.20  
  Purchase #6 $60.30   4.126%   $62.788   $62.79   $62.80   $62.80  
  Purchase #7 $85.99   9.356%   $94.0352   $94.04   $94.05   $94.00  
  7 purchase totals = $1,109.60       $1,177.3082   $1,177.32   $1,177.35   $1,177.40