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 $118.42   13.761%   $134.7158   $134.72   $134.70   $134.70  
  Purchase #2 $118.72   5.673%   $125.455   $125.46   $125.45   $125.50  
  Purchase #3 $13.58   8.640%   $14.7533   $14.75   $14.75   $14.80  
  Purchase #4 $131.62   8.695%   $143.0644   $143.06   $143.05   $143.10  
  Purchase #5 $163.69   4.480%   $171.0233   $171.02   $171.00   $171.00  
  Purchase #6 $175.97   4.771%   $184.3655   $184.37   $184.35   $184.40  
  Purchase #7 $234.78   7.618%   $252.6655   $252.67   $252.65   $252.70  
  7 purchase totals = $956.78       $1,026.0428   $1,026.05   $1,025.95   $1,026.20