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 $124.93   13.352%   $141.6107   $141.61   $141.60   $141.60  
  Purchase #2 $147.35   11.297%   $163.9961   $164.00   $164.00   $164.00  
  Purchase #3 $43.80   9.349%   $47.8949   $47.89   $47.90   $47.90  
  Purchase #4 $6.52   11.186%   $7.2493   $7.25   $7.25   $7.20  
  Purchase #5 $193.27   5.667%   $204.2226   $204.22   $204.20   $204.20  
  Purchase #6 $132.65   12.140%   $148.7537   $148.75   $148.75   $148.80  
  Purchase #7 $72.94   6.166%   $77.4375   $77.44   $77.45   $77.40  
  7 purchase totals = $721.46       $791.1648   $791.16   $791.15   $791.10