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 $47.31   12.635%   $53.2876   $53.29   $53.30   $53.30  
  Purchase #2 $244.89   13.361%   $277.6098   $277.61   $277.60   $277.60  
  Purchase #3 $38.76   7.728%   $41.7554   $41.76   $41.75   $41.80  
  Purchase #4 $85.61   8.833%   $93.1719   $93.17   $93.15   $93.20  
  Purchase #5 $142.88   7.801%   $154.0261   $154.03   $154.05   $154.00  
  Purchase #6 $243.96   5.631%   $257.6974   $257.70   $257.70   $257.70  
  Purchase #7 $137.53   5.504%   $145.0997   $145.10   $145.10   $145.10  
  7 purchase totals = $940.94       $1,022.6479   $1,022.66   $1,022.65   $1,022.70