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 $88.78   9.857%   $97.531   $97.53   $97.55   $97.50  
  Purchase #2 $161.97   7.641%   $174.3461   $174.35   $174.35   $174.30  
  Purchase #3 $91.57   3.227%   $94.525   $94.53   $94.55   $94.50  
  Purchase #4 $136.95   3.456%   $141.683   $141.68   $141.70   $141.70  
  Purchase #5 $234.89   10.225%   $258.9075   $258.91   $258.90   $258.90  
  Purchase #6 $196.75   3.855%   $204.3347   $204.33   $204.35   $204.30  
  Purchase #7 $96.80   11.579%   $108.0085   $108.01   $108.00   $108.00  
  7 purchase totals = $1,007.71       $1,079.3358   $1,079.34   $1,079.40   $1,079.20