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 $58.52   8.321%   $63.3894   $63.39   $63.40   $63.40  
  Purchase #2 $121.33   10.604%   $134.1958   $134.20   $134.20   $134.20  
  Purchase #3 $162.53   4.160%   $169.2912   $169.29   $169.30   $169.30  
  Purchase #4 $81.49   5.235%   $85.756   $85.76   $85.75   $85.80  
  Purchase #5 $89.87   8.870%   $97.8415   $97.84   $97.85   $97.80  
  Purchase #6 $112.48   3.219%   $116.1007   $116.10   $116.10   $116.10  
  Purchase #7 $35.52   13.630%   $40.3614   $40.36   $40.35   $40.40  
  7 purchase totals = $661.74       $706.9360   $706.94   $706.95   $707.00