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 $87.85   5.871%   $93.0077   $93.01   $93.00   $93.00  
  Purchase #2 $211.36   4.256%   $220.3555   $220.36   $220.35   $220.40  
  Purchase #3 $101.59   13.319%   $115.1208   $115.12   $115.10   $115.10  
  Purchase #4 $63.83   6.295%   $67.8481   $67.85   $67.85   $67.80  
  Purchase #5 $65.25   7.769%   $70.3193   $70.32   $70.30   $70.30  
  Purchase #6 $96.56   6.795%   $103.1213   $103.12   $103.10   $103.10  
  Purchase #7 $250.47   5.126%   $263.3091   $263.31   $263.30   $263.30  
  7 purchase totals = $876.91       $933.0818   $933.09   $933.00   $933.00