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 $54.97   11.588%   $61.3399   $61.34   $61.35   $61.30  
  Purchase #2 $14.41   4.463%   $15.0531   $15.05   $15.05   $15.10  
  Purchase #3 $65.78   12.558%   $74.0407   $74.04   $74.05   $74.00  
  Purchase #4 $241.27   7.831%   $260.1639   $260.16   $260.15   $260.20  
  Purchase #5 $28.68   8.223%   $31.0384   $31.04   $31.05   $31.00  
  Purchase #6 $210.80   8.192%   $228.0687   $228.07   $228.05   $228.10  
  Purchase #7 $243.87   10.522%   $269.53   $269.53   $269.55   $269.50  
  7 purchase totals = $859.78       $939.2347   $939.23   $939.25   $939.20