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 $83.84   8.777%   $91.1986   $91.20   $91.20   $91.20  
  Purchase #2 $105.96   6.704%   $113.0636   $113.06   $113.05   $113.10  
  Purchase #3 $24.51   8.807%   $26.6686   $26.67   $26.65   $26.70  
  Purchase #4 $140.93   6.365%   $149.9002   $149.90   $149.90   $149.90  
  Purchase #5 $88.96   6.352%   $94.6107   $94.61   $94.60   $94.60  
  Purchase #6 $182.37   6.440%   $194.1146   $194.11   $194.10   $194.10  
  Purchase #7 $73.66   8.222%   $79.7163   $79.72   $79.70   $79.70  
  7 purchase totals = $700.23       $749.2726   $749.27   $749.20   $749.30