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 $61.51   8.182%   $66.5427   $66.54   $66.55   $66.50  
  Purchase #2 $236.80   3.761%   $245.706   $245.71   $245.70   $245.70  
  Purchase #3 $63.82   4.863%   $66.9236   $66.92   $66.90   $66.90  
  Purchase #4 $14.30   12.471%   $16.0834   $16.08   $16.10   $16.10  
  Purchase #5 $180.47   11.408%   $201.058   $201.06   $201.05   $201.10  
  Purchase #6 $80.67   12.501%   $90.7546   $90.75   $90.75   $90.80  
  Purchase #7 $96.70   12.499%   $108.7865   $108.79   $108.80   $108.80  
  7 purchase totals = $734.27       $795.8548   $795.85   $795.85   $795.90