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 $147.76   9.634%   $161.9952   $162.00   $162.00   $162.00  
  Purchase #2 $124.56   12.824%   $140.5336   $140.53   $140.55   $140.50  
  Purchase #3 $229.89   5.448%   $242.4144   $242.41   $242.40   $242.40  
  Purchase #4 $174.83   11.139%   $194.3043   $194.30   $194.30   $194.30  
  Purchase #5 $105.31   9.302%   $115.1059   $115.11   $115.10   $115.10  
  Purchase #6 $107.92   5.189%   $113.52   $113.52   $113.50   $113.50  
  Purchase #7 $60.40   11.709%   $67.4722   $67.47   $67.45   $67.50  
  7 purchase totals = $950.67       $1,035.3456   $1,035.34   $1,035.30   $1,035.30