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 $68.68   12.359%   $77.1682   $77.17   $77.15   $77.20  
  Purchase #2 $82.27   7.647%   $88.5612   $88.56   $88.55   $88.60  
  Purchase #3 $171.85   7.827%   $185.3007   $185.30   $185.30   $185.30  
  Purchase #4 $247.56   5.562%   $261.3293   $261.33   $261.35   $261.30  
  Purchase #5 $48.68   10.542%   $53.8118   $53.81   $53.80   $53.80  
  Purchase #6 $205.87   7.255%   $220.8059   $220.81   $220.80   $220.80  
  Purchase #7 $168.84   7.183%   $180.9678   $180.97   $180.95   $181.00  
  7 purchase totals = $993.75       $1,067.9449   $1,067.95   $1,067.90   $1,068.00