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 $83.71   8.781%   $91.0606   $91.06   $91.05   $91.10  
  Purchase #2 $150.47   4.825%   $157.7302   $157.73   $157.75   $157.70  
  Purchase #3 $215.69   11.590%   $240.6885   $240.69   $240.70   $240.70  
  Purchase #4 $74.49   10.435%   $82.263   $82.26   $82.25   $82.30  
  Purchase #5 $163.59   4.143%   $170.3675   $170.37   $170.35   $170.40  
  Purchase #6 $178.92   12.662%   $201.5749   $201.57   $201.55   $201.60  
  Purchase #7 $65.71   7.314%   $70.516   $70.52   $70.50   $70.50  
  7 purchase totals = $932.58       $1,014.2007   $1,014.20   $1,014.15   $1,014.30