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 $209.98   13.205%   $237.7079   $237.71   $237.70   $237.70  
  Purchase #2 $36.97   4.122%   $38.4939   $38.49   $38.50   $38.50  
  Purchase #3 $85.35   6.746%   $91.1077   $91.11   $91.10   $91.10  
  Purchase #4 $179.74   4.296%   $187.4616   $187.46   $187.45   $187.50  
  Purchase #5 $240.27   3.473%   $248.6146   $248.61   $248.60   $248.60  
  Purchase #6 $38.98   11.756%   $43.5625   $43.56   $43.55   $43.60  
  Purchase #7 $162.93   7.319%   $174.8548   $174.85   $174.85   $174.90  
  7 purchase totals = $954.22       $1,021.8030   $1,021.79   $1,021.75   $1,021.90