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 $248.25   11.442%   $276.6548   $276.65   $276.65   $276.70  
  Purchase #2 $229.43   7.245%   $246.0522   $246.05   $246.05   $246.10  
  Purchase #3 $168.52   4.870%   $176.7269   $176.73   $176.75   $176.70  
  Purchase #4 $226.30   4.667%   $236.8614   $236.86   $236.85   $236.90  
  Purchase #5 $210.60   10.827%   $233.4017   $233.40   $233.40   $233.40  
  Purchase #6 $57.35   5.132%   $60.2932   $60.29   $60.30   $60.30  
  Purchase #7 $100.70   10.370%   $111.1426   $111.14   $111.15   $111.10  
  7 purchase totals = $1,241.15       $1,341.1328   $1,341.12   $1,341.15   $1,341.20