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 $193.82   6.146%   $205.7322   $205.73   $205.75   $205.70  
  Purchase #2 $63.86   13.780%   $72.6599   $72.66   $72.65   $72.70  
  Purchase #3 $232.61   3.452%   $240.6397   $240.64   $240.65   $240.60  
  Purchase #4 $26.98   9.152%   $29.4492   $29.45   $29.45   $29.40  
  Purchase #5 $17.82   9.256%   $19.4694   $19.47   $19.45   $19.50  
  Purchase #6 $238.40   9.711%   $261.551   $261.55   $261.55   $261.60  
  Purchase #7 $201.54   13.297%   $228.3388   $228.34   $228.35   $228.30  
  7 purchase totals = $975.03       $1,057.8402   $1,057.84   $1,057.85   $1,057.80