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 $168.98   12.772%   $190.5621   $190.56   $190.55   $190.60  
  Purchase #2 $141.86   6.845%   $151.5703   $151.57   $151.55   $151.60  
  Purchase #3 $167.31   5.628%   $176.7262   $176.73   $176.75   $176.70  
  Purchase #4 $24.25   4.770%   $25.4067   $25.41   $25.40   $25.40  
  Purchase #5 $109.41   11.802%   $122.3226   $122.32   $122.30   $122.30  
  Purchase #6 $184.69   5.586%   $195.0068   $195.01   $195.00   $195.00  
  Purchase #7 $169.51   7.234%   $181.7724   $181.77   $181.75   $181.80  
  7 purchase totals = $966.01       $1,043.3671   $1,043.37   $1,043.30   $1,043.40