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 $246.59   9.111%   $269.0568   $269.06   $269.05   $269.10  
  Purchase #2 $155.72   8.820%   $169.4545   $169.45   $169.45   $169.50  
  Purchase #3 $57.40   9.472%   $62.8369   $62.84   $62.85   $62.80  
  Purchase #4 $211.48   8.274%   $228.9779   $228.98   $229.00   $229.00  
  Purchase #5 $146.73   10.828%   $162.6179   $162.62   $162.60   $162.60  
  Purchase #6 $186.55   8.403%   $202.2258   $202.23   $202.25   $202.20  
  Purchase #7 $132.72   9.786%   $145.708   $145.71   $145.70   $145.70  
  7 purchase totals = $1,137.19       $1,240.8778   $1,240.89   $1,240.90   $1,240.90