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 $117.85   7.327%   $126.4849   $126.48   $126.50   $126.50  
  Purchase #2 $147.58   12.460%   $165.9685   $165.97   $165.95   $166.00  
  Purchase #3 $112.95   11.477%   $125.9133   $125.91   $125.90   $125.90  
  Purchase #4 $245.60   11.182%   $273.063   $273.06   $273.05   $273.10  
  Purchase #5 $120.31   10.191%   $132.5708   $132.57   $132.55   $132.60  
  Purchase #6 $150.83   10.170%   $166.1694   $166.17   $166.15   $166.20  
  Purchase #7 $59.85   12.523%   $67.345   $67.35   $67.35   $67.30  
  7 purchase totals = $954.97       $1,057.5149   $1,057.51   $1,057.45   $1,057.60