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 $235.28   10.296%   $259.5044   $259.50   $259.50   $259.50  
  Purchase #2 $200.53   9.635%   $219.8511   $219.85   $219.85   $219.90  
  Purchase #3 $17.64   10.783%   $19.5421   $19.54   $19.55   $19.50  
  Purchase #4 $234.75   4.791%   $245.9969   $246.00   $246.00   $246.00  
  Purchase #5 $22.54   5.843%   $23.857   $23.86   $23.85   $23.90  
  Purchase #6 $85.79   10.831%   $95.0819   $95.08   $95.10   $95.10  
  Purchase #7 $229.88   6.364%   $244.5096   $244.51   $244.50   $244.50  
  7 purchase totals = $1,026.41       $1,108.3430   $1,108.34   $1,108.35   $1,108.40