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 $60.83   5.712%   $64.3046   $64.30   $64.30   $64.30  
  Purchase #2 $222.52   8.662%   $241.7947   $241.79   $241.80   $241.80  
  Purchase #3 $221.55   7.714%   $238.6404   $238.64   $238.65   $238.60  
  Purchase #4 $103.70   12.662%   $116.8305   $116.83   $116.85   $116.80  
  Purchase #5 $225.97   4.238%   $235.5466   $235.55   $235.55   $235.50  
  Purchase #6 $221.63   5.781%   $234.4424   $234.44   $234.45   $234.40  
  Purchase #7 $117.53   4.225%   $122.4956   $122.50   $122.50   $122.50  
  7 purchase totals = $1,173.73       $1,254.0548   $1,254.05   $1,254.10   $1,253.90