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 $178.87   13.782%   $203.5219   $203.52   $203.50   $203.50  
  Purchase #2 $246.56   13.656%   $280.2302   $280.23   $280.25   $280.20  
  Purchase #3 $148.72   3.358%   $153.714   $153.71   $153.70   $153.70  
  Purchase #4 $117.28   7.222%   $125.75   $125.75   $125.75   $125.80  
  Purchase #5 $92.65   10.454%   $102.3356   $102.34   $102.35   $102.30  
  Purchase #6 $54.74   5.119%   $57.5421   $57.54   $57.55   $57.50  
  Purchase #7 $88.61   3.396%   $91.6192   $91.62   $91.60   $91.60  
  7 purchase totals = $927.43       $1,014.7130   $1,014.71   $1,014.70   $1,014.60