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 $56.63   8.660%   $61.5342   $61.53   $61.55   $61.50  
  Purchase #2 $221.70   7.708%   $238.7886   $238.79   $238.80   $238.80  
  Purchase #3 $198.66   9.862%   $218.2518   $218.25   $218.25   $218.30  
  Purchase #4 $53.29   7.162%   $57.1066   $57.11   $57.10   $57.10  
  Purchase #5 $7.83   8.121%   $8.4659   $8.47   $8.45   $8.50  
  Purchase #6 $5.55   3.218%   $5.7286   $5.73   $5.75   $5.70  
  Purchase #7 $170.29   5.350%   $179.4005   $179.40   $179.40   $179.40  
  7 purchase totals = $713.95       $769.2762   $769.28   $769.30   $769.30