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 $101.99   5.203%   $107.2965   $107.30   $107.30   $107.30  
  Purchase #2 $169.85   6.183%   $180.3518   $180.35   $180.35   $180.40  
  Purchase #3 $175.75   12.585%   $197.8681   $197.87   $197.85   $197.90  
  Purchase #4 $148.27   13.335%   $168.0418   $168.04   $168.05   $168.00  
  Purchase #5 $199.81   4.581%   $208.9633   $208.96   $208.95   $209.00  
  Purchase #6 $168.84   10.642%   $186.808   $186.81   $186.80   $186.80  
  Purchase #7 $5.31   4.201%   $5.5331   $5.53   $5.55   $5.50  
  7 purchase totals = $969.82       $1,054.8626   $1,054.86   $1,054.85   $1,054.90