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 $74.45   12.662%   $83.8769   $83.88   $83.90   $83.90  
  Purchase #2 $162.86   7.674%   $175.3579   $175.36   $175.35   $175.40  
  Purchase #3 $93.54   4.662%   $97.9008   $97.90   $97.90   $97.90  
  Purchase #4 $71.70   5.337%   $75.5266   $75.53   $75.55   $75.50  
  Purchase #5 $165.34   6.872%   $176.7022   $176.70   $176.70   $176.70  
  Purchase #6 $110.85   9.293%   $121.1513   $121.15   $121.15   $121.20  
  Purchase #7 $220.57   5.198%   $232.0352   $232.04   $232.05   $232.00  
  7 purchase totals = $899.31       $962.5509   $962.56   $962.60   $962.60