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 $196.52   7.469%   $211.1981   $211.20   $211.20   $211.20  
  Purchase #2 $57.48   13.200%   $65.0674   $65.07   $65.05   $65.10  
  Purchase #3 $19.76   7.409%   $21.224   $21.22   $21.20   $21.20  
  Purchase #4 $156.36   5.683%   $165.2459   $165.25   $165.25   $165.20  
  Purchase #5 $161.61   12.591%   $181.9583   $181.96   $181.95   $182.00  
  Purchase #6 $104.79   11.397%   $116.7329   $116.73   $116.75   $116.70  
  Purchase #7 $11.27   5.864%   $11.9309   $11.93   $11.95   $11.90  
  7 purchase totals = $707.79       $773.3575   $773.36   $773.35   $773.30