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 $144.86   13.673%   $164.6667   $164.67   $164.65   $164.70  
  Purchase #2 $161.54   11.272%   $179.7488   $179.75   $179.75   $179.70  
  Purchase #3 $20.66   6.476%   $21.9979   $22.00   $22.00   $22.00  
  Purchase #4 $192.75   9.652%   $211.3542   $211.35   $211.35   $211.40  
  Purchase #5 $145.76   4.793%   $152.7463   $152.75   $152.75   $152.70  
  Purchase #6 $20.36   3.288%   $21.0294   $21.03   $21.05   $21.00  
  Purchase #7 $145.86   13.702%   $165.8457   $165.85   $165.85   $165.80  
  7 purchase totals = $831.79       $917.3890   $917.40   $917.40   $917.30