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 $58.74   5.184%   $61.7851   $61.79   $61.80   $61.80  
  Purchase #2 $156.76   13.133%   $177.3473   $177.35   $177.35   $177.30  
  Purchase #3 $197.76   10.234%   $217.9988   $218.00   $218.00   $218.00  
  Purchase #4 $70.52   9.461%   $77.1919   $77.19   $77.20   $77.20  
  Purchase #5 $31.47   4.174%   $32.7836   $32.78   $32.80   $32.80  
  Purchase #6 $191.37   8.693%   $208.0058   $208.01   $208.00   $208.00  
  Purchase #7 $92.73   10.129%   $102.1226   $102.12   $102.10   $102.10  
  7 purchase totals = $799.35       $877.2351   $877.24   $877.25   $877.20