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 $57.85   5.779%   $61.1932   $61.19   $61.20   $61.20  
  Purchase #2 $27.50   3.224%   $28.3866   $28.39   $28.40   $28.40  
  Purchase #3 $234.98   8.379%   $254.669   $254.67   $254.65   $254.70  
  Purchase #4 $125.66   12.235%   $141.0345   $141.03   $141.05   $141.00  
  Purchase #5 $83.25   11.829%   $93.0976   $93.10   $93.10   $93.10  
  Purchase #6 $222.80   8.740%   $242.2727   $242.27   $242.25   $242.30  
  Purchase #7 $234.34   3.303%   $242.0803   $242.08   $242.10   $242.10  
  7 purchase totals = $986.38       $1,062.7339   $1,062.73   $1,062.75   $1,062.80