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 $235.55   7.647%   $253.5625   $253.56   $253.55   $253.60  
  Purchase #2 $62.47   11.303%   $69.531   $69.53   $69.55   $69.50  
  Purchase #3 $24.29   7.677%   $26.1547   $26.15   $26.15   $26.20  
  Purchase #4 $176.54   9.228%   $192.8311   $192.83   $192.85   $192.80  
  Purchase #5 $203.30   13.195%   $230.1254   $230.13   $230.15   $230.10  
  Purchase #6 $60.91   9.264%   $66.5527   $66.55   $66.55   $66.60  
  Purchase #7 $169.95   6.492%   $180.9832   $180.98   $181.00   $181.00  
  7 purchase totals = $933.01       $1,019.7406   $1,019.73   $1,019.80   $1,019.80