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 $158.71   5.563%   $167.539   $167.54   $167.55   $167.50  
  Purchase #2 $24.60   3.517%   $25.4652   $25.47   $25.45   $25.50  
  Purchase #3 $53.53   10.241%   $59.012   $59.01   $59.00   $59.00  
  Purchase #4 $204.28   5.566%   $215.6502   $215.65   $215.65   $215.70  
  Purchase #5 $111.71   8.569%   $121.2824   $121.28   $121.30   $121.30  
  Purchase #6 $91.86   6.345%   $97.6885   $97.69   $97.70   $97.70  
  Purchase #7 $8.93   11.585%   $9.9645   $9.96   $9.95   $10.00  
  7 purchase totals = $653.62       $696.6018   $696.60   $696.60   $696.70