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 $75.85   9.631%   $83.1551   $83.16   $83.15   $83.20  
  Purchase #2 $85.91   9.565%   $94.1273   $94.13   $94.15   $94.10  
  Purchase #3 $154.38   12.398%   $173.52   $173.52   $173.50   $173.50  
  Purchase #4 $87.87   8.850%   $95.6465   $95.65   $95.65   $95.60  
  Purchase #5 $163.91   7.314%   $175.8984   $175.90   $175.90   $175.90  
  Purchase #6 $189.65   13.142%   $214.5738   $214.57   $214.55   $214.60  
  Purchase #7 $163.67   6.627%   $174.5164   $174.52   $174.50   $174.50  
  7 purchase totals = $921.24       $1,011.4375   $1,011.45   $1,011.40   $1,011.40