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 $179.76   8.570%   $195.1654   $195.17   $195.15   $195.20  
  Purchase #2 $130.70   6.841%   $139.6412   $139.64   $139.65   $139.60  
  Purchase #3 $50.31   4.489%   $52.5684   $52.57   $52.55   $52.60  
  Purchase #4 $248.94   5.696%   $263.1196   $263.12   $263.10   $263.10  
  Purchase #5 $116.26   4.371%   $121.3417   $121.34   $121.35   $121.30  
  Purchase #6 $95.58   11.621%   $106.6874   $106.69   $106.70   $106.70  
  Purchase #7 $36.51   5.690%   $38.5874   $38.59   $38.60   $38.60  
  7 purchase totals = $858.06       $917.1111   $917.12   $917.10   $917.10