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 $154.74   12.457%   $174.016   $174.02   $174.00   $174.00  
  Purchase #2 $230.86   4.742%   $241.8074   $241.81   $241.80   $241.80  
  Purchase #3 $18.98   9.457%   $20.7749   $20.77   $20.75   $20.80  
  Purchase #4 $211.90   9.283%   $231.5707   $231.57   $231.55   $231.60  
  Purchase #5 $106.65   5.685%   $112.7131   $112.71   $112.70   $112.70  
  Purchase #6 $121.44   6.631%   $129.4927   $129.49   $129.50   $129.50  
  Purchase #7 $34.26   11.611%   $38.2379   $38.24   $38.25   $38.20  
  7 purchase totals = $878.83       $948.6127   $948.61   $948.55   $948.60