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 $24.86   8.845%   $27.0589   $27.06   $27.05   $27.10  
  Purchase #2 $197.88   3.399%   $204.6059   $204.61   $204.60   $204.60  
  Purchase #3 $37.72   3.745%   $39.1326   $39.13   $39.15   $39.10  
  Purchase #4 $220.46   12.790%   $248.6568   $248.66   $248.65   $248.70  
  Purchase #5 $216.71   6.123%   $229.9792   $229.98   $230.00   $230.00  
  Purchase #6 $63.78   3.397%   $65.9466   $65.95   $65.95   $65.90  
  Purchase #7 $191.85   4.174%   $199.8578   $199.86   $199.85   $199.90  
  7 purchase totals = $953.26       $1,015.2378   $1,015.25   $1,015.25   $1,015.30