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 $245.84   5.752%   $259.9807   $259.98   $260.00   $260.00  
  Purchase #2 $169.45   11.426%   $188.8114   $188.81   $188.80   $188.80  
  Purchase #3 $173.38   11.588%   $193.4713   $193.47   $193.45   $193.50  
  Purchase #4 $126.34   9.694%   $138.5874   $138.59   $138.60   $138.60  
  Purchase #5 $89.98   6.300%   $95.6487   $95.65   $95.65   $95.60  
  Purchase #6 $108.31   12.645%   $122.0058   $122.01   $122.00   $122.00  
  Purchase #7 $52.79   12.685%   $59.4864   $59.49   $59.50   $59.50  
  7 purchase totals = $966.09       $1,057.9917   $1,058.00   $1,058.00   $1,058.00