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 $178.82   4.574%   $186.9992   $187.00   $187.00   $187.00  
  Purchase #2 $64.63   11.161%   $71.8434   $71.84   $71.85   $71.80  
  Purchase #3 $232.65   4.671%   $243.5171   $243.52   $243.50   $243.50  
  Purchase #4 $56.53   7.516%   $60.7788   $60.78   $60.80   $60.80  
  Purchase #5 $98.70   5.153%   $103.786   $103.79   $103.80   $103.80  
  Purchase #6 $80.81   3.199%   $83.3951   $83.40   $83.40   $83.40  
  Purchase #7 $71.53   4.767%   $74.9398   $74.94   $74.95   $74.90  
  7 purchase totals = $783.67       $825.2594   $825.27   $825.30   $825.20