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 $188.65   8.121%   $203.9703   $203.97   $203.95   $204.00  
  Purchase #2 $76.34   8.690%   $82.9739   $82.97   $82.95   $83.00  
  Purchase #3 $185.34   11.158%   $206.0202   $206.02   $206.00   $206.00  
  Purchase #4 $104.39   13.307%   $118.2812   $118.28   $118.30   $118.30  
  Purchase #5 $249.60   3.230%   $257.6621   $257.66   $257.65   $257.70  
  Purchase #6 $239.85   13.811%   $272.9757   $272.98   $273.00   $273.00  
  Purchase #7 $55.54   11.265%   $61.7966   $61.80   $61.80   $61.80  
  7 purchase totals = $1,099.71       $1,203.6800   $1,203.68   $1,203.65   $1,203.80