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 $146.70   10.175%   $161.6267   $161.63   $161.65   $161.60  
  Purchase #2 $53.34   9.627%   $58.475   $58.48   $58.50   $58.50  
  Purchase #3 $236.53   13.208%   $267.7709   $267.77   $267.75   $267.80  
  Purchase #4 $39.77   4.857%   $41.7016   $41.70   $41.70   $41.70  
  Purchase #5 $183.88   9.865%   $202.0198   $202.02   $202.00   $202.00  
  Purchase #6 $233.59   4.575%   $244.2767   $244.28   $244.30   $244.30  
  Purchase #7 $37.34   3.135%   $38.5106   $38.51   $38.50   $38.50  
  7 purchase totals = $931.15       $1,014.3813   $1,014.39   $1,014.40   $1,014.40