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 $207.80   13.394%   $235.6327   $235.63   $235.65   $235.60  
  Purchase #2 $225.73   9.645%   $247.5017   $247.50   $247.50   $247.50  
  Purchase #3 $128.33   9.328%   $140.3006   $140.30   $140.30   $140.30  
  Purchase #4 $42.36   3.173%   $43.7041   $43.70   $43.70   $43.70  
  Purchase #5 $70.91   3.738%   $73.5606   $73.56   $73.55   $73.60  
  Purchase #6 $245.78   10.674%   $272.0146   $272.01   $272.00   $272.00  
  Purchase #7 $91.90   6.683%   $98.0417   $98.04   $98.05   $98.00  
  7 purchase totals = $1,012.81       $1,110.7560   $1,110.74   $1,110.75   $1,110.70