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 $152.66   9.611%   $167.3322   $167.33   $167.35   $167.30  
  Purchase #2 $93.93   13.607%   $106.7111   $106.71   $106.70   $106.70  
  Purchase #3 $34.94   6.422%   $37.1838   $37.18   $37.20   $37.20  
  Purchase #4 $209.72   12.859%   $236.6879   $236.69   $236.70   $236.70  
  Purchase #5 $248.86   12.424%   $279.7784   $279.78   $279.80   $279.80  
  Purchase #6 $165.93   12.578%   $186.8007   $186.80   $186.80   $186.80  
  Purchase #7 $49.90   4.669%   $52.2298   $52.23   $52.25   $52.20  
  7 purchase totals = $955.94       $1,066.7239   $1,066.72   $1,066.80   $1,066.70