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 $84.61   11.233%   $94.1142   $94.11   $94.10   $94.10  
  Purchase #2 $219.37   8.657%   $238.3609   $238.36   $238.35   $238.40  
  Purchase #3 $185.67   8.557%   $201.5578   $201.56   $201.55   $201.60  
  Purchase #4 $23.77   12.407%   $26.7191   $26.72   $26.70   $26.70  
  Purchase #5 $179.40   12.748%   $202.2699   $202.27   $202.25   $202.30  
  Purchase #6 $75.39   13.616%   $85.6551   $85.66   $85.65   $85.70  
  Purchase #7 $206.47   11.122%   $229.4336   $229.43   $229.45   $229.40  
  7 purchase totals = $974.68       $1,078.1106   $1,078.11   $1,078.05   $1,078.20