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 $128.62   5.722%   $135.9796   $135.98   $136.00   $136.00  
  Purchase #2 $95.46   8.774%   $103.8357   $103.84   $103.85   $103.80  
  Purchase #3 $69.94   11.384%   $77.902   $77.90   $77.90   $77.90  
  Purchase #4 $172.96   12.339%   $194.3015   $194.30   $194.30   $194.30  
  Purchase #5 $156.49   4.585%   $163.6651   $163.67   $163.65   $163.70  
  Purchase #6 $23.40   10.705%   $25.905   $25.91   $25.90   $25.90  
  Purchase #7 $140.70   7.788%   $151.6577   $151.66   $151.65   $151.70  
  7 purchase totals = $787.57       $853.2466   $853.26   $853.25   $853.30