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 $91.79   4.477%   $95.8994   $95.90   $95.90   $95.90  
  Purchase #2 $240.51   12.542%   $270.6748   $270.67   $270.65   $270.70  
  Purchase #3 $249.69   7.332%   $267.9973   $268.00   $268.00   $268.00  
  Purchase #4 $159.62   8.774%   $173.6251   $173.63   $173.65   $173.60  
  Purchase #5 $54.61   9.445%   $59.7679   $59.77   $59.75   $59.80  
  Purchase #6 $109.72   12.649%   $123.5985   $123.60   $123.60   $123.60  
  Purchase #7 $20.80   9.619%   $22.8008   $22.80   $22.80   $22.80  
  7 purchase totals = $926.74       $1,014.3638   $1,014.37   $1,014.35   $1,014.40