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 $195.94   12.438%   $220.311   $220.31   $220.30   $220.30  
  Purchase #2 $133.43   3.759%   $138.4456   $138.45   $138.45   $138.40  
  Purchase #3 $59.72   8.795%   $64.9724   $64.97   $64.95   $65.00  
  Purchase #4 $167.73   10.721%   $185.7123   $185.71   $185.70   $185.70  
  Purchase #5 $57.53   6.240%   $61.1199   $61.12   $61.10   $61.10  
  Purchase #6 $211.56   4.591%   $221.2727   $221.27   $221.25   $221.30  
  Purchase #7 $157.26   12.697%   $177.2273   $177.23   $177.25   $177.20  
  7 purchase totals = $983.17       $1,069.0612   $1,069.06   $1,069.00   $1,069.00