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 $168.39   11.119%   $187.1133   $187.11   $187.10   $187.10  
  Purchase #2 $234.83   9.404%   $256.9134   $256.91   $256.90   $256.90  
  Purchase #3 $61.45   6.760%   $65.604   $65.60   $65.60   $65.60  
  Purchase #4 $77.60   3.866%   $80.6   $80.60   $80.60   $80.60  
  Purchase #5 $244.46   13.590%   $277.6821   $277.68   $277.70   $277.70  
  Purchase #6 $113.81   6.494%   $121.2008   $121.20   $121.20   $121.20  
  Purchase #7 $107.55   5.180%   $113.1211   $113.12   $113.10   $113.10  
  7 purchase totals = $1,008.09       $1,102.2347   $1,102.22   $1,102.20   $1,102.20