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 $83.85   8.481%   $90.9613   $90.96   $90.95   $91.00  
  Purchase #2 $136.60   4.858%   $143.236   $143.24   $143.25   $143.20  
  Purchase #3 $72.76   5.591%   $76.828   $76.83   $76.85   $76.80  
  Purchase #4 $241.78   7.277%   $259.3743   $259.37   $259.35   $259.40  
  Purchase #5 $120.97   12.227%   $135.761   $135.76   $135.75   $135.80  
  Purchase #6 $123.74   9.824%   $135.8962   $135.90   $135.90   $135.90  
  Purchase #7 $206.94   6.211%   $219.793   $219.79   $219.80   $219.80  
  7 purchase totals = $986.64       $1,061.8498   $1,061.85   $1,061.85   $1,061.90