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 $53.92   12.334%   $60.5705   $60.57   $60.55   $60.60  
  Purchase #2 $229.97   7.414%   $247.02   $247.02   $247.00   $247.00  
  Purchase #3 $211.40   6.278%   $224.6717   $224.67   $224.65   $224.70  
  Purchase #4 $75.62   12.599%   $85.1474   $85.15   $85.15   $85.10  
  Purchase #5 $125.80   4.686%   $131.695   $131.70   $131.70   $131.70  
  Purchase #6 $112.56   9.651%   $123.4232   $123.42   $123.40   $123.40  
  Purchase #7 $75.70   12.397%   $85.0845   $85.08   $85.10   $85.10  
  7 purchase totals = $884.97       $957.6123   $957.61   $957.55   $957.60