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 $114.96   9.247%   $125.5904   $125.59   $125.60   $125.60  
  Purchase #2 $94.61   13.773%   $107.6406   $107.64   $107.65   $107.60  
  Purchase #3 $241.86   5.251%   $254.5601   $254.56   $254.55   $254.60  
  Purchase #4 $149.73   12.502%   $168.4492   $168.45   $168.45   $168.40  
  Purchase #5 $143.97   11.804%   $160.9642   $160.96   $160.95   $161.00  
  Purchase #6 $60.81   10.255%   $67.0461   $67.05   $67.05   $67.00  
  Purchase #7 $123.26   10.291%   $135.9447   $135.94   $135.95   $135.90  
  7 purchase totals = $929.20       $1,020.1953   $1,020.19   $1,020.20   $1,020.10