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 $179.60   12.458%   $201.9746   $201.97   $201.95   $202.00  
  Purchase #2 $141.84   12.450%   $159.4991   $159.50   $159.50   $159.50  
  Purchase #3 $25.29   3.377%   $26.144   $26.14   $26.15   $26.10  
  Purchase #4 $13.55   11.547%   $15.1146   $15.11   $15.10   $15.10  
  Purchase #5 $108.41   11.684%   $121.0766   $121.08   $121.10   $121.10  
  Purchase #6 $176.51   10.207%   $194.5264   $194.53   $194.55   $194.50  
  Purchase #7 $57.37   11.268%   $63.8345   $63.83   $63.85   $63.80  
  7 purchase totals = $702.57       $782.1698   $782.16   $782.20   $782.10