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 $69.57   6.278%   $73.9376   $73.94   $73.95   $73.90  
  Purchase #2 $111.82   13.200%   $126.5802   $126.58   $126.60   $126.60  
  Purchase #3 $57.61   12.511%   $64.8176   $64.82   $64.80   $64.80  
  Purchase #4 $135.97   8.518%   $147.5519   $147.55   $147.55   $147.60  
  Purchase #5 $24.28   10.415%   $26.8088   $26.81   $26.80   $26.80  
  Purchase #6 $222.62   6.752%   $237.6513   $237.65   $237.65   $237.70  
  Purchase #7 $77.89   12.188%   $87.3832   $87.38   $87.40   $87.40  
  7 purchase totals = $699.76       $764.7306   $764.73   $764.75   $764.80