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 $69.65   8.503%   $75.5723   $75.57   $75.55   $75.60  
  Purchase #2 $167.86   6.266%   $178.3781   $178.38   $178.40   $178.40  
  Purchase #3 $98.56   3.534%   $102.0431   $102.04   $102.05   $102.00  
  Purchase #4 $200.79   5.178%   $211.1869   $211.19   $211.20   $211.20  
  Purchase #5 $70.72   4.509%   $73.9088   $73.91   $73.90   $73.90  
  Purchase #6 $246.46   9.155%   $269.0234   $269.02   $269.00   $269.00  
  Purchase #7 $77.31   9.411%   $84.5856   $84.59   $84.60   $84.60  
  7 purchase totals = $931.35       $994.6982   $994.70   $994.70   $994.70