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 $234.70   11.759%   $262.2984   $262.30   $262.30   $262.30  
  Purchase #2 $96.96   9.811%   $106.4727   $106.47   $106.45   $106.50  
  Purchase #3 $59.91   10.459%   $66.176   $66.18   $66.20   $66.20  
  Purchase #4 $120.88   3.818%   $125.4952   $125.50   $125.50   $125.50  
  Purchase #5 $215.64   7.867%   $232.6044   $232.60   $232.60   $232.60  
  Purchase #6 $172.44   4.791%   $180.7016   $180.70   $180.70   $180.70  
  Purchase #7 $123.46   8.170%   $133.5467   $133.55   $133.55   $133.50  
  7 purchase totals = $1,023.99       $1,107.2950   $1,107.30   $1,107.30   $1,107.30