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 $166.77   12.398%   $187.4461   $187.45   $187.45   $187.40  
  Purchase #2 $134.66   6.733%   $143.7267   $143.73   $143.75   $143.70  
  Purchase #3 $119.74   4.395%   $125.0026   $125.00   $125.00   $125.00  
  Purchase #4 $128.82   3.272%   $133.035   $133.04   $133.05   $133.00  
  Purchase #5 $232.95   6.479%   $248.0428   $248.04   $248.05   $248.00  
  Purchase #6 $119.66   5.206%   $125.8895   $125.89   $125.90   $125.90  
  Purchase #7 $59.31   6.873%   $63.3864   $63.39   $63.40   $63.40  
  7 purchase totals = $961.91       $1,026.5291   $1,026.54   $1,026.60   $1,026.40