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 $135.69   4.817%   $142.2262   $142.23   $142.25   $142.20  
  Purchase #2 $5.50   10.600%   $6.083   $6.08   $6.10   $6.10  
  Purchase #3 $7.91   10.729%   $8.7587   $8.76   $8.75   $8.80  
  Purchase #4 $124.73   7.459%   $134.0336   $134.03   $134.05   $134.00  
  Purchase #5 $194.83   12.110%   $218.4239   $218.42   $218.40   $218.40  
  Purchase #6 $11.72   4.395%   $12.2351   $12.24   $12.25   $12.20  
  Purchase #7 $28.60   8.326%   $30.9812   $30.98   $31.00   $31.00  
  7 purchase totals = $508.98       $552.7417   $552.74   $552.80   $552.70