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 $241.72   7.854%   $260.7047   $260.70   $260.70   $260.70  
  Purchase #2 $186.98   8.140%   $202.2002   $202.20   $202.20   $202.20  
  Purchase #3 $98.54   7.176%   $105.6112   $105.61   $105.60   $105.60  
  Purchase #4 $194.30   8.690%   $211.1847   $211.18   $211.20   $211.20  
  Purchase #5 $165.50   5.563%   $174.7068   $174.71   $174.70   $174.70  
  Purchase #6 $14.30   4.331%   $14.9193   $14.92   $14.90   $14.90  
  Purchase #7 $38.40   13.700%   $43.6608   $43.66   $43.65   $43.70  
  7 purchase totals = $939.74       $1,012.9877   $1,012.98   $1,012.95   $1,013.00