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 $69.92   5.731%   $73.9271   $73.93   $73.95   $73.90  
  Purchase #2 $246.95   8.771%   $268.61   $268.61   $268.60   $268.60  
  Purchase #3 $130.77   7.577%   $140.6784   $140.68   $140.70   $140.70  
  Purchase #4 $191.39   3.604%   $198.2877   $198.29   $198.30   $198.30  
  Purchase #5 $193.49   8.352%   $209.6503   $209.65   $209.65   $209.70  
  Purchase #6 $220.92   10.351%   $243.7874   $243.79   $243.80   $243.80  
  Purchase #7 $91.79   10.779%   $101.684   $101.68   $101.70   $101.70  
  7 purchase totals = $1,145.23       $1,236.6249   $1,236.63   $1,236.70   $1,236.70