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 $198.77   6.179%   $211.052   $211.05   $211.05   $211.10  
  Purchase #2 $97.41   4.766%   $102.0526   $102.05   $102.05   $102.10  
  Purchase #3 $58.32   12.758%   $65.7605   $65.76   $65.75   $65.80  
  Purchase #4 $136.57   5.848%   $144.5566   $144.56   $144.55   $144.60  
  Purchase #5 $84.75   8.330%   $91.8097   $91.81   $91.80   $91.80  
  Purchase #6 $231.62   5.731%   $244.8941   $244.89   $244.90   $244.90  
  Purchase #7 $154.33   3.596%   $159.8797   $159.88   $159.90   $159.90  
  7 purchase totals = $961.77       $1,020.0052   $1,020.00   $1,020.00   $1,020.20