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 $62.48   5.383%   $65.8433   $65.84   $65.85   $65.80  
  Purchase #2 $161.51   5.205%   $169.9166   $169.92   $169.90   $169.90  
  Purchase #3 $203.87   9.706%   $223.6576   $223.66   $223.65   $223.70  
  Purchase #4 $187.76   8.627%   $203.9581   $203.96   $203.95   $204.00  
  Purchase #5 $162.42   11.821%   $181.6197   $181.62   $181.60   $181.60  
  Purchase #6 $232.92   7.174%   $249.6297   $249.63   $249.65   $249.60  
  Purchase #7 $201.52   5.796%   $213.2001   $213.20   $213.20   $213.20  
  7 purchase totals = $1,212.48       $1,307.8251   $1,307.83   $1,307.80   $1,307.80