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 $68.57   10.718%   $75.9193   $75.92   $75.90   $75.90  
  Purchase #2 $201.97   8.568%   $219.2748   $219.27   $219.25   $219.30  
  Purchase #3 $11.35   12.868%   $12.8105   $12.81   $12.80   $12.80  
  Purchase #4 $189.93   10.811%   $210.4633   $210.46   $210.45   $210.50  
  Purchase #5 $68.26   8.513%   $74.071   $74.07   $74.05   $74.10  
  Purchase #6 $223.93   13.275%   $253.6567   $253.66   $253.65   $253.70  
  Purchase #7 $213.93   12.245%   $240.1257   $240.13   $240.15   $240.10  
  7 purchase totals = $977.94       $1,086.3213   $1,086.32   $1,086.25   $1,086.40