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 $146.82   13.581%   $166.7596   $166.76   $166.75   $166.80  
  Purchase #2 $229.62   10.424%   $253.5556   $253.56   $253.55   $253.60  
  Purchase #3 $138.57   3.757%   $143.7761   $143.78   $143.80   $143.80  
  Purchase #4 $177.94   13.853%   $202.59   $202.59   $202.60   $202.60  
  Purchase #5 $118.51   9.864%   $130.1998   $130.20   $130.20   $130.20  
  Purchase #6 $129.41   11.310%   $144.0463   $144.05   $144.05   $144.00  
  Purchase #7 $56.41   9.152%   $61.5726   $61.57   $61.55   $61.60  
  7 purchase totals = $997.28       $1,102.5000   $1,102.51   $1,102.50   $1,102.60