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 $209.27   11.590%   $233.5244   $233.52   $233.50   $233.50  
  Purchase #2 $191.81   6.136%   $203.5795   $203.58   $203.60   $203.60  
  Purchase #3 $139.60   6.736%   $149.0035   $149.00   $149.00   $149.00  
  Purchase #4 $153.37   13.856%   $174.6209   $174.62   $174.60   $174.60  
  Purchase #5 $192.54   5.289%   $202.7234   $202.72   $202.70   $202.70  
  Purchase #6 $27.57   11.362%   $30.7025   $30.70   $30.70   $30.70  
  Purchase #7 $114.44   11.136%   $127.184   $127.18   $127.20   $127.20  
  7 purchase totals = $1,028.60       $1,121.3382   $1,121.32   $1,121.30   $1,121.30