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 $58.64   11.494%   $65.3801   $65.38   $65.40   $65.40  
  Purchase #2 $207.65   5.845%   $219.7871   $219.79   $219.80   $219.80  
  Purchase #3 $205.80   11.382%   $229.2242   $229.22   $229.20   $229.20  
  Purchase #4 $210.47   11.867%   $235.4465   $235.45   $235.45   $235.40  
  Purchase #5 $57.29   9.342%   $62.642   $62.64   $62.65   $62.60  
  Purchase #6 $220.75   12.739%   $248.8713   $248.87   $248.85   $248.90  
  Purchase #7 $166.72   9.114%   $181.9149   $181.91   $181.90   $181.90  
  7 purchase totals = $1,127.32       $1,243.2661   $1,243.26   $1,243.25   $1,243.20