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 $104.94   12.671%   $118.2369   $118.24   $118.25   $118.20  
  Purchase #2 $33.63   4.315%   $35.0811   $35.08   $35.10   $35.10  
  Purchase #3 $223.64   3.590%   $231.6687   $231.67   $231.65   $231.70  
  Purchase #4 $104.99   5.563%   $110.8306   $110.83   $110.85   $110.80  
  Purchase #5 $242.29   9.175%   $264.5201   $264.52   $264.50   $264.50  
  Purchase #6 $231.89   4.474%   $242.2648   $242.26   $242.25   $242.30  
  Purchase #7 $191.35   13.186%   $216.5814   $216.58   $216.60   $216.60  
  7 purchase totals = $1,132.73       $1,219.1836   $1,219.18   $1,219.20   $1,219.20