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 $101.47   13.507%   $115.1756   $115.18   $115.20   $115.20  
  Purchase #2 $124.50   11.573%   $138.9084   $138.91   $138.90   $138.90  
  Purchase #3 $198.85   9.257%   $217.2575   $217.26   $217.25   $217.30  
  Purchase #4 $249.91   9.470%   $273.5765   $273.58   $273.60   $273.60  
  Purchase #5 $223.68   13.681%   $254.2817   $254.28   $254.30   $254.30  
  Purchase #6 $90.25   13.764%   $102.672   $102.67   $102.65   $102.70  
  Purchase #7 $63.90   13.852%   $72.7514   $72.75   $72.75   $72.80  
  7 purchase totals = $1,052.56       $1,174.6231   $1,174.63   $1,174.65   $1,174.80