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 $246.31   6.545%   $262.431   $262.43   $262.45   $262.40  
  Purchase #2 $172.96   6.734%   $184.6071   $184.61   $184.60   $184.60  
  Purchase #3 $127.86   4.432%   $133.5268   $133.53   $133.55   $133.50  
  Purchase #4 $27.93   6.654%   $29.7885   $29.79   $29.80   $29.80  
  Purchase #5 $152.44   5.822%   $161.3151   $161.32   $161.30   $161.30  
  Purchase #6 $39.66   12.359%   $44.5616   $44.56   $44.55   $44.60  
  Purchase #7 $15.35   10.619%   $16.98   $16.98   $17.00   $17.00  
  7 purchase totals = $782.51       $833.2101   $833.22   $833.25   $833.20