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 $219.41   6.843%   $234.4242   $234.42   $234.40   $234.40  
  Purchase #2 $138.95   4.641%   $145.3987   $145.40   $145.40   $145.40  
  Purchase #3 $161.88   6.860%   $172.985   $172.99   $173.00   $173.00  
  Purchase #4 $153.40   5.581%   $161.9613   $161.96   $161.95   $162.00  
  Purchase #5 $247.75   7.775%   $267.0126   $267.01   $267.00   $267.00  
  Purchase #6 $142.92   7.201%   $153.2117   $153.21   $153.20   $153.20  
  Purchase #7 $76.71   8.585%   $83.2956   $83.30   $83.30   $83.30  
  7 purchase totals = $1,141.02       $1,218.2891   $1,218.29   $1,218.25   $1,218.30