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 $239.62   9.582%   $262.5804   $262.58   $262.60   $262.60  
  Purchase #2 $80.79   7.519%   $86.8646   $86.86   $86.85   $86.90  
  Purchase #3 $202.90   9.432%   $222.0375   $222.04   $222.05   $222.00  
  Purchase #4 $166.74   13.833%   $189.8051   $189.81   $189.80   $189.80  
  Purchase #5 $84.65   3.721%   $87.7998   $87.80   $87.80   $87.80  
  Purchase #6 $154.67   9.582%   $169.4905   $169.49   $169.50   $169.50  
  Purchase #7 $68.96   10.198%   $75.9925   $75.99   $76.00   $76.00  
  7 purchase totals = $998.33       $1,094.5704   $1,094.57   $1,094.60   $1,094.60