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 $41.33   8.479%   $44.8344   $44.83   $44.85   $44.80  
  Purchase #2 $166.45   11.615%   $185.7832   $185.78   $185.80   $185.80  
  Purchase #3 $219.85   11.206%   $244.4864   $244.49   $244.50   $244.50  
  Purchase #4 $187.92   12.470%   $211.3536   $211.35   $211.35   $211.40  
  Purchase #5 $113.92   10.238%   $125.5831   $125.58   $125.60   $125.60  
  Purchase #6 $205.96   7.541%   $221.4914   $221.49   $221.50   $221.50  
  Purchase #7 $227.36   6.682%   $242.5522   $242.55   $242.55   $242.60  
  7 purchase totals = $1,162.79       $1,276.0843   $1,276.07   $1,276.15   $1,276.20