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 $95.61   5.285%   $100.663   $100.66   $100.65   $100.70  
  Purchase #2 $161.56   5.744%   $170.84   $170.84   $170.85   $170.80  
  Purchase #3 $239.25   3.138%   $246.7577   $246.76   $246.75   $246.80  
  Purchase #4 $212.81   7.260%   $228.26   $228.26   $228.25   $228.30  
  Purchase #5 $184.64   11.637%   $206.1266   $206.13   $206.15   $206.10  
  Purchase #6 $64.31   8.681%   $69.8928   $69.89   $69.90   $69.90  
  Purchase #7 $206.42   5.816%   $218.4254   $218.43   $218.45   $218.40  
  7 purchase totals = $1,164.60       $1,240.9655   $1,240.97   $1,241.00   $1,241.00