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 $73.38   12.700%   $82.6993   $82.70   $82.70   $82.70  
  Purchase #2 $58.61   11.638%   $65.431   $65.43   $65.45   $65.40  
  Purchase #3 $100.52   4.330%   $104.8725   $104.87   $104.85   $104.90  
  Purchase #4 $167.97   8.818%   $182.7816   $182.78   $182.80   $182.80  
  Purchase #5 $213.48   9.748%   $234.29   $234.29   $234.30   $234.30  
  Purchase #6 $60.36   5.274%   $63.5434   $63.54   $63.55   $63.50  
  Purchase #7 $248.44   11.166%   $276.1808   $276.18   $276.20   $276.20  
  7 purchase totals = $922.76       $1,009.7986   $1,009.79   $1,009.85   $1,009.80