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 $50.74   12.614%   $57.1403   $57.14   $57.15   $57.10  
  Purchase #2 $172.86   12.640%   $194.7095   $194.71   $194.70   $194.70  
  Purchase #3 $227.74   7.830%   $245.572   $245.57   $245.55   $245.60  
  Purchase #4 $244.35   9.736%   $268.1399   $268.14   $268.15   $268.10  
  Purchase #5 $183.87   10.282%   $202.7755   $202.78   $202.80   $202.80  
  Purchase #6 $164.25   6.820%   $175.4519   $175.45   $175.45   $175.50  
  Purchase #7 $80.87   13.470%   $91.7632   $91.76   $91.75   $91.80  
  7 purchase totals = $1,124.68       $1,235.5523   $1,235.55   $1,235.55   $1,235.60