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 $145.92   13.429%   $165.5156   $165.52   $165.50   $165.50  
  Purchase #2 $183.64   5.452%   $193.6521   $193.65   $193.65   $193.70  
  Purchase #3 $83.98   4.363%   $87.644   $87.64   $87.65   $87.60  
  Purchase #4 $93.31   5.179%   $98.1425   $98.14   $98.15   $98.10  
  Purchase #5 $222.71   11.455%   $248.2214   $248.22   $248.20   $248.20  
  Purchase #6 $144.43   6.420%   $153.7024   $153.70   $153.70   $153.70  
  Purchase #7 $217.88   12.134%   $244.3176   $244.32   $244.30   $244.30  
  7 purchase totals = $1,091.87       $1,191.1956   $1,191.19   $1,191.15   $1,191.10