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 $86.27   11.454%   $96.1514   $96.15   $96.15   $96.20  
  Purchase #2 $229.70   9.459%   $251.4273   $251.43   $251.45   $251.40  
  Purchase #3 $148.26   5.861%   $156.9495   $156.95   $156.95   $156.90  
  Purchase #4 $24.76   3.421%   $25.607   $25.61   $25.60   $25.60  
  Purchase #5 $40.25   13.442%   $45.6604   $45.66   $45.65   $45.70  
  Purchase #6 $224.41   9.107%   $244.847   $244.85   $244.85   $244.80  
  Purchase #7 $224.69   5.441%   $236.9154   $236.92   $236.90   $236.90  
  7 purchase totals = $978.34       $1,057.5580   $1,057.57   $1,057.55   $1,057.50