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 $156.69   4.768%   $164.161   $164.16   $164.15   $164.20  
  Purchase #2 $10.38   7.506%   $11.1591   $11.16   $11.15   $11.20  
  Purchase #3 $120.67   7.290%   $129.4668   $129.47   $129.45   $129.50  
  Purchase #4 $203.75   10.227%   $224.5875   $224.59   $224.60   $224.60  
  Purchase #5 $75.44   12.113%   $84.578   $84.58   $84.60   $84.60  
  Purchase #6 $35.26   10.564%   $38.9849   $38.98   $39.00   $39.00  
  Purchase #7 $193.56   4.729%   $202.7135   $202.71   $202.70   $202.70  
  7 purchase totals = $795.75       $855.6508   $855.65   $855.65   $855.80