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 $184.31   9.380%   $201.5983   $201.60   $201.60   $201.60  
  Purchase #2 $52.56   4.697%   $55.0287   $55.03   $55.05   $55.00  
  Purchase #3 $107.37   10.669%   $118.8253   $118.83   $118.85   $118.80  
  Purchase #4 $134.64   5.605%   $142.1866   $142.19   $142.20   $142.20  
  Purchase #5 $88.48   7.830%   $95.408   $95.41   $95.40   $95.40  
  Purchase #6 $128.60   5.727%   $135.9649   $135.96   $135.95   $136.00  
  Purchase #7 $50.79   7.520%   $54.6094   $54.61   $54.60   $54.60  
  7 purchase totals = $746.75       $803.6212   $803.63   $803.65   $803.60