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 $250.83   6.449%   $267.006   $267.01   $267.00   $267.00  
  Purchase #2 $20.82   9.155%   $22.7261   $22.73   $22.75   $22.70  
  Purchase #3 $41.61   8.860%   $45.2966   $45.30   $45.30   $45.30  
  Purchase #4 $214.60   3.135%   $221.3277   $221.33   $221.35   $221.30  
  Purchase #5 $14.57   3.793%   $15.1226   $15.12   $15.10   $15.10  
  Purchase #6 $168.68   13.316%   $191.1414   $191.14   $191.15   $191.10  
  Purchase #7 $58.30   12.861%   $65.798   $65.80   $65.80   $65.80  
  7 purchase totals = $769.41       $828.4184   $828.43   $828.45   $828.30