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 $92.72   3.653%   $96.1071   $96.11   $96.10   $96.10  
  Purchase #2 $8.26   4.320%   $8.6168   $8.62   $8.60   $8.60  
  Purchase #3 $15.59   11.322%   $17.3551   $17.36   $17.35   $17.40  
  Purchase #4 $25.80   3.607%   $26.7306   $26.73   $26.75   $26.70  
  Purchase #5 $169.34   13.740%   $192.6073   $192.61   $192.60   $192.60  
  Purchase #6 $77.53   13.305%   $87.8454   $87.85   $87.85   $87.80  
  Purchase #7 $172.99   7.243%   $185.5197   $185.52   $185.50   $185.50  
  7 purchase totals = $562.23       $614.7820   $614.80   $614.75   $614.70