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 $23.49   8.835%   $25.5653   $25.57   $25.55   $25.60  
  Purchase #2 $90.98   12.568%   $102.4144   $102.41   $102.40   $102.40  
  Purchase #3 $232.64   5.312%   $244.9978   $245.00   $245.00   $245.00  
  Purchase #4 $231.61   5.199%   $243.6514   $243.65   $243.65   $243.70  
  Purchase #5 $211.31   13.781%   $240.4306   $240.43   $240.45   $240.40  
  Purchase #6 $144.50   11.784%   $161.5279   $161.53   $161.55   $161.50  
  Purchase #7 $225.33   10.261%   $248.4511   $248.45   $248.45   $248.50  
  7 purchase totals = $1,159.86       $1,267.0385   $1,267.04   $1,267.05   $1,267.10