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 $177.59   7.770%   $191.3887   $191.39   $191.40   $191.40  
  Purchase #2 $133.36   5.588%   $140.8122   $140.81   $140.80   $140.80  
  Purchase #3 $41.31   12.122%   $46.3176   $46.32   $46.30   $46.30  
  Purchase #4 $62.31   13.788%   $70.9013   $70.90   $70.90   $70.90  
  Purchase #5 $106.93   7.767%   $115.2353   $115.24   $115.25   $115.20  
  Purchase #6 $232.81   5.781%   $246.2687   $246.27   $246.25   $246.30  
  Purchase #7 $203.88   5.590%   $215.2769   $215.28   $215.30   $215.30  
  7 purchase totals = $958.19       $1,026.2007   $1,026.21   $1,026.20   $1,026.20