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 $175.89   5.567%   $185.6818   $185.68   $185.70   $185.70  
  Purchase #2 $19.39   13.631%   $22.0331   $22.03   $22.05   $22.00  
  Purchase #3 $24.90   3.701%   $25.8215   $25.82   $25.80   $25.80  
  Purchase #4 $56.46   6.271%   $60.0006   $60.00   $60.00   $60.00  
  Purchase #5 $121.55   3.170%   $125.4031   $125.40   $125.40   $125.40  
  Purchase #6 $207.97   5.832%   $220.0988   $220.10   $220.10   $220.10  
  Purchase #7 $239.80   6.714%   $255.9002   $255.90   $255.90   $255.90  
  7 purchase totals = $845.96       $894.9391   $894.93   $894.95   $894.90