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 $250.78   13.275%   $284.071   $284.07   $284.05   $284.10  
  Purchase #2 $214.31   8.596%   $232.7321   $232.73   $232.75   $232.70  
  Purchase #3 $43.79   8.685%   $47.5932   $47.59   $47.60   $47.60  
  Purchase #4 $143.91   12.578%   $162.011   $162.01   $162.00   $162.00  
  Purchase #5 $205.36   5.171%   $215.9792   $215.98   $216.00   $216.00  
  Purchase #6 $32.32   3.212%   $33.3581   $33.36   $33.35   $33.40  
  Purchase #7 $70.34   5.831%   $74.4415   $74.44   $74.45   $74.40  
  7 purchase totals = $960.81       $1,050.1861   $1,050.18   $1,050.20   $1,050.20