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 $117.40   8.192%   $127.0174   $127.02   $127.00   $127.00  
  Purchase #2 $235.97   6.204%   $250.6096   $250.61   $250.60   $250.60  
  Purchase #3 $110.97   13.527%   $125.9809   $125.98   $126.00   $126.00  
  Purchase #4 $194.69   9.228%   $212.656   $212.66   $212.65   $212.70  
  Purchase #5 $66.49   11.357%   $74.0413   $74.04   $74.05   $74.00  
  Purchase #6 $174.91   13.549%   $198.6086   $198.61   $198.60   $198.60  
  Purchase #7 $93.87   11.538%   $104.7007   $104.70   $104.70   $104.70  
  7 purchase totals = $994.30       $1,093.6145   $1,093.62   $1,093.60   $1,093.60