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 $77.41   10.741%   $85.7246   $85.72   $85.70   $85.70  
  Purchase #2 $17.49   7.204%   $18.75   $18.75   $18.75   $18.80  
  Purchase #3 $187.41   12.594%   $211.0124   $211.01   $211.00   $211.00  
  Purchase #4 $26.58   9.461%   $29.0947   $29.09   $29.10   $29.10  
  Purchase #5 $226.42   7.305%   $242.96   $242.96   $242.95   $243.00  
  Purchase #6 $226.27   8.126%   $244.6567   $244.66   $244.65   $244.70  
  Purchase #7 $75.83   8.262%   $82.0951   $82.10   $82.10   $82.10  
  7 purchase totals = $837.41       $914.2935   $914.29   $914.25   $914.40