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 $69.93   4.448%   $73.0405   $73.04   $73.05   $73.00  
  Purchase #2 $93.49   10.472%   $103.2803   $103.28   $103.30   $103.30  
  Purchase #3 $55.39   6.231%   $58.8414   $58.84   $58.85   $58.80  
  Purchase #4 $193.33   10.421%   $213.4769   $213.48   $213.50   $213.50  
  Purchase #5 $88.35   3.378%   $91.3345   $91.33   $91.35   $91.30  
  Purchase #6 $244.46   4.183%   $254.6858   $254.69   $254.70   $254.70  
  Purchase #7 $54.93   6.681%   $58.5999   $58.60   $58.60   $58.60  
  7 purchase totals = $799.88       $853.2593   $853.26   $853.35   $853.20