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 $99.83   13.547%   $113.354   $113.35   $113.35   $113.40  
  Purchase #2 $32.50   6.434%   $34.5911   $34.59   $34.60   $34.60  
  Purchase #3 $156.28   12.194%   $175.3368   $175.34   $175.35   $175.30  
  Purchase #4 $226.53   7.171%   $242.7745   $242.77   $242.75   $242.80  
  Purchase #5 $247.89   6.351%   $263.6335   $263.63   $263.65   $263.60  
  Purchase #6 $29.65   6.668%   $31.6271   $31.63   $31.65   $31.60  
  Purchase #7 $182.66   13.413%   $207.1602   $207.16   $207.15   $207.20  
  7 purchase totals = $975.34       $1,068.4772   $1,068.47   $1,068.50   $1,068.50