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 $84.75   13.586%   $96.2641   $96.26   $96.25   $96.30  
  Purchase #2 $6.84   11.577%   $7.6319   $7.63   $7.65   $7.60  
  Purchase #3 $210.99   12.464%   $237.2878   $237.29   $237.30   $237.30  
  Purchase #4 $195.80   11.743%   $218.7928   $218.79   $218.80   $218.80  
  Purchase #5 $102.64   4.262%   $107.0145   $107.01   $107.00   $107.00  
  Purchase #6 $130.30   4.340%   $135.955   $135.96   $135.95   $136.00  
  Purchase #7 $229.99   12.776%   $259.3735   $259.37   $259.35   $259.40  
  7 purchase totals = $961.31       $1,062.3196   $1,062.31   $1,062.30   $1,062.40