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 $119.96   12.499%   $134.9538   $134.95   $134.95   $135.00  
  Purchase #2 $201.33   12.173%   $225.8379   $225.84   $225.85   $225.80  
  Purchase #3 $46.81   10.346%   $51.653   $51.65   $51.65   $51.70  
  Purchase #4 $66.51   6.811%   $71.04   $71.04   $71.05   $71.00  
  Purchase #5 $244.65   12.298%   $274.7371   $274.74   $274.75   $274.70  
  Purchase #6 $189.67   9.815%   $208.2861   $208.29   $208.30   $208.30  
  Purchase #7 $24.90   6.810%   $26.5957   $26.60   $26.60   $26.60  
  7 purchase totals = $893.83       $993.1036   $993.11   $993.15   $993.10