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 $30.73   10.726%   $34.0261   $34.03   $34.05   $34.00  
  Purchase #2 $237.73   8.341%   $257.5591   $257.56   $257.55   $257.60  
  Purchase #3 $133.85   10.324%   $147.6687   $147.67   $147.65   $147.70  
  Purchase #4 $139.91   4.727%   $146.5235   $146.52   $146.50   $146.50  
  Purchase #5 $167.81   5.697%   $177.3701   $177.37   $177.35   $177.40  
  Purchase #6 $163.66   11.707%   $182.8197   $182.82   $182.80   $182.80  
  Purchase #7 $95.60   7.386%   $102.661   $102.66   $102.65   $102.70  
  7 purchase totals = $969.29       $1,048.6282   $1,048.63   $1,048.55   $1,048.70