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 $106.73   9.563%   $116.9366   $116.94   $116.95   $116.90  
  Purchase #2 $99.91   12.275%   $112.174   $112.17   $112.15   $112.20  
  Purchase #3 $180.98   10.588%   $200.1422   $200.14   $200.15   $200.10  
  Purchase #4 $5.55   5.183%   $5.8377   $5.84   $5.85   $5.80  
  Purchase #5 $215.95   5.847%   $228.5766   $228.58   $228.60   $228.60  
  Purchase #6 $123.80   7.478%   $133.0578   $133.06   $133.05   $133.10  
  Purchase #7 $188.87   9.144%   $206.1403   $206.14   $206.15   $206.10  
  7 purchase totals = $921.79       $1,002.8652   $1,002.87   $1,002.90   $1,002.80