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 $245.31   11.831%   $274.3326   $274.33   $274.35   $274.30  
  Purchase #2 $164.60   12.199%   $184.6796   $184.68   $184.70   $184.70  
  Purchase #3 $41.27   10.823%   $45.7367   $45.74   $45.75   $45.70  
  Purchase #4 $193.98   6.836%   $207.2405   $207.24   $207.25   $207.20  
  Purchase #5 $73.47   5.169%   $77.2677   $77.27   $77.25   $77.30  
  Purchase #6 $194.46   6.184%   $206.4854   $206.49   $206.50   $206.50  
  Purchase #7 $177.73   3.397%   $183.7675   $183.77   $183.75   $183.80  
  7 purchase totals = $1,090.82       $1,179.5100   $1,179.52   $1,179.55   $1,179.50