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 $112.91   5.268%   $118.8581   $118.86   $118.85   $118.90  
  Purchase #2 $91.99   3.785%   $95.4718   $95.47   $95.45   $95.50  
  Purchase #3 $82.72   10.219%   $91.1732   $91.17   $91.15   $91.20  
  Purchase #4 $101.80   5.480%   $107.3786   $107.38   $107.40   $107.40  
  Purchase #5 $135.77   10.696%   $150.292   $150.29   $150.30   $150.30  
  Purchase #6 $219.97   13.783%   $250.2885   $250.29   $250.30   $250.30  
  Purchase #7 $211.52   5.330%   $222.794   $222.79   $222.80   $222.80  
  7 purchase totals = $956.68       $1,036.2562   $1,036.25   $1,036.25   $1,036.40