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 $243.29   12.872%   $274.6063   $274.61   $274.60   $274.60  
  Purchase #2 $233.85   13.477%   $265.366   $265.37   $265.35   $265.40  
  Purchase #3 $203.32   12.144%   $228.0112   $228.01   $228.00   $228.00  
  Purchase #4 $32.80   5.548%   $34.6197   $34.62   $34.60   $34.60  
  Purchase #5 $95.84   9.798%   $105.2304   $105.23   $105.25   $105.20  
  Purchase #6 $181.78   6.723%   $194.0011   $194.00   $194.00   $194.00  
  Purchase #7 $61.54   6.718%   $65.6743   $65.67   $65.65   $65.70  
  7 purchase totals = $1,052.42       $1,167.5090   $1,167.51   $1,167.45   $1,167.50