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 $88.33   8.320%   $95.6791   $95.68   $95.70   $95.70  
  Purchase #2 $227.64   5.857%   $240.9729   $240.97   $240.95   $241.00  
  Purchase #3 $211.50   6.320%   $224.8668   $224.87   $224.85   $224.90  
  Purchase #4 $105.78   12.362%   $118.8565   $118.86   $118.85   $118.90  
  Purchase #5 $63.58   3.687%   $65.9242   $65.92   $65.90   $65.90  
  Purchase #6 $76.69   9.357%   $83.8659   $83.87   $83.85   $83.90  
  Purchase #7 $148.89   9.445%   $162.9527   $162.95   $162.95   $163.00  
  7 purchase totals = $922.41       $993.1181   $993.12   $993.05   $993.30