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 $238.84   10.451%   $263.8012   $263.80   $263.80   $263.80  
  Purchase #2 $169.81   7.672%   $182.8378   $182.84   $182.85   $182.80  
  Purchase #3 $56.27   5.829%   $59.55   $59.55   $59.55   $59.60  
  Purchase #4 $84.59   4.418%   $88.3272   $88.33   $88.35   $88.30  
  Purchase #5 $181.41   7.315%   $194.6801   $194.68   $194.70   $194.70  
  Purchase #6 $44.64   5.836%   $47.2452   $47.25   $47.25   $47.20  
  Purchase #7 $215.27   4.607%   $225.1875   $225.19   $225.20   $225.20  
  7 purchase totals = $990.83       $1,061.6290   $1,061.64   $1,061.70   $1,061.60