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 $91.62   13.564%   $104.0473   $104.05   $104.05   $104.00  
  Purchase #2 $215.63   5.514%   $227.5198   $227.52   $227.50   $227.50  
  Purchase #3 $201.77   4.377%   $210.6015   $210.60   $210.60   $210.60  
  Purchase #4 $92.37   3.203%   $95.3286   $95.33   $95.35   $95.30  
  Purchase #5 $98.48   8.307%   $106.6607   $106.66   $106.65   $106.70  
  Purchase #6 $220.56   3.201%   $227.6201   $227.62   $227.60   $227.60  
  Purchase #7 $33.93   8.231%   $36.7228   $36.72   $36.70   $36.70  
  7 purchase totals = $954.36       $1,008.5008   $1,008.50   $1,008.45   $1,008.40