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 $207.49   6.463%   $220.9001   $220.90   $220.90   $220.90  
  Purchase #2 $77.42   8.587%   $84.0681   $84.07   $84.05   $84.10  
  Purchase #3 $73.57   13.191%   $83.2746   $83.27   $83.25   $83.30  
  Purchase #4 $70.82   9.142%   $77.2944   $77.29   $77.30   $77.30  
  Purchase #5 $238.38   6.829%   $254.659   $254.66   $254.65   $254.70  
  Purchase #6 $215.80   8.772%   $234.73   $234.73   $234.75   $234.70  
  Purchase #7 $158.33   8.489%   $171.7706   $171.77   $171.75   $171.80  
  7 purchase totals = $1,041.81       $1,126.6968   $1,126.69   $1,126.65   $1,126.80