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 $117.33   9.728%   $128.7439   $128.74   $128.75   $128.70  
  Purchase #2 $8.47   12.527%   $9.531   $9.53   $9.55   $9.50  
  Purchase #3 $92.25   5.599%   $97.4151   $97.42   $97.40   $97.40  
  Purchase #4 $35.45   4.310%   $36.9779   $36.98   $37.00   $37.00  
  Purchase #5 $185.34   7.476%   $199.196   $199.20   $199.20   $199.20  
  Purchase #6 $141.41   6.150%   $150.1067   $150.11   $150.10   $150.10  
  Purchase #7 $139.60   5.694%   $147.5488   $147.55   $147.55   $147.50  
  7 purchase totals = $719.85       $769.5194   $769.53   $769.55   $769.40