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 $97.26   5.636%   $102.7416   $102.74   $102.75   $102.70  
  Purchase #2 $17.78   8.618%   $19.3123   $19.31   $19.30   $19.30  
  Purchase #3 $129.61   9.216%   $141.5549   $141.55   $141.55   $141.60  
  Purchase #4 $129.82   5.151%   $136.507   $136.51   $136.50   $136.50  
  Purchase #5 $206.52   8.236%   $223.529   $223.53   $223.55   $223.50  
  Purchase #6 $97.49   4.304%   $101.686   $101.69   $101.70   $101.70  
  Purchase #7 $14.30   10.786%   $15.8424   $15.84   $15.85   $15.80  
  7 purchase totals = $692.78       $741.1732   $741.17   $741.20   $741.10