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 $50.55   8.294%   $54.7426   $54.74   $54.75   $54.70  
  Purchase #2 $111.99   3.227%   $115.6039   $115.60   $115.60   $115.60  
  Purchase #3 $178.76   7.536%   $192.2314   $192.23   $192.25   $192.20  
  Purchase #4 $216.93   5.493%   $228.846   $228.85   $228.85   $228.80  
  Purchase #5 $53.80   5.144%   $56.5675   $56.57   $56.55   $56.60  
  Purchase #6 $166.65   8.431%   $180.7003   $180.70   $180.70   $180.70  
  Purchase #7 $8.92   4.378%   $9.3105   $9.31   $9.30   $9.30  
  7 purchase totals = $787.60       $838.0022   $838.00   $838.00   $837.90