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 $214.56   12.412%   $241.1912   $241.19   $241.20   $241.20  
  Purchase #2 $132.97   9.692%   $145.8575   $145.86   $145.85   $145.90  
  Purchase #3 $24.60   6.238%   $26.1345   $26.13   $26.15   $26.10  
  Purchase #4 $92.83   4.274%   $96.7976   $96.80   $96.80   $96.80  
  Purchase #5 $152.70   8.401%   $165.5283   $165.53   $165.55   $165.50  
  Purchase #6 $111.96   3.177%   $115.517   $115.52   $115.50   $115.50  
  Purchase #7 $243.38   7.503%   $261.6408   $261.64   $261.65   $261.60  
  7 purchase totals = $973.00       $1,052.6669   $1,052.67   $1,052.70   $1,052.60