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 $124.57   9.173%   $135.9968   $136.00   $136.00   $136.00  
  Purchase #2 $15.60   11.218%   $17.35   $17.35   $17.35   $17.40  
  Purchase #3 $231.73   4.717%   $242.6607   $242.66   $242.65   $242.70  
  Purchase #4 $107.33   8.382%   $116.3264   $116.33   $116.35   $116.30  
  Purchase #5 $106.26   12.283%   $119.3119   $119.31   $119.30   $119.30  
  Purchase #6 $184.70   10.126%   $203.4027   $203.40   $203.40   $203.40  
  Purchase #7 $183.39   4.257%   $191.1969   $191.20   $191.20   $191.20  
  7 purchase totals = $953.58       $1,026.2454   $1,026.25   $1,026.25   $1,026.30