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 $65.29   4.822%   $68.4383   $68.44   $68.45   $68.40  
  Purchase #2 $185.81   8.204%   $201.0539   $201.05   $201.05   $201.10  
  Purchase #3 $210.95   5.872%   $223.337   $223.34   $223.35   $223.30  
  Purchase #4 $210.30   5.408%   $221.673   $221.67   $221.65   $221.70  
  Purchase #5 $118.42   9.649%   $129.8463   $129.85   $129.85   $129.80  
  Purchase #6 $184.74   9.647%   $202.5619   $202.56   $202.55   $202.60  
  Purchase #7 $11.69   8.611%   $12.6966   $12.70   $12.70   $12.70  
  7 purchase totals = $987.20       $1,059.6070   $1,059.61   $1,059.60   $1,059.60