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 $120.52   7.446%   $129.4939   $129.49   $129.50   $129.50  
  Purchase #2 $106.26   7.540%   $114.272   $114.27   $114.25   $114.30  
  Purchase #3 $243.82   5.845%   $258.0713   $258.07   $258.05   $258.10  
  Purchase #4 $21.60   5.126%   $22.7072   $22.71   $22.70   $22.70  
  Purchase #5 $115.56   3.862%   $120.0229   $120.02   $120.00   $120.00  
  Purchase #6 $7.54   7.102%   $8.0755   $8.08   $8.10   $8.10  
  Purchase #7 $141.31   9.550%   $154.8051   $154.81   $154.80   $154.80  
  7 purchase totals = $756.61       $807.4479   $807.45   $807.40   $807.50