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 $194.70   6.604%   $207.558   $207.56   $207.55   $207.60  
  Purchase #2 $202.52   3.294%   $209.191   $209.19   $209.20   $209.20  
  Purchase #3 $63.30   3.322%   $65.4028   $65.40   $65.40   $65.40  
  Purchase #4 $214.28   5.729%   $226.5561   $226.56   $226.55   $226.60  
  Purchase #5 $200.46   12.321%   $225.1587   $225.16   $225.15   $225.20  
  Purchase #6 $72.43   9.478%   $79.2949   $79.29   $79.30   $79.30  
  Purchase #7 $65.56   4.452%   $68.4787   $68.48   $68.50   $68.50  
  7 purchase totals = $1,013.25       $1,081.6402   $1,081.64   $1,081.65   $1,081.80