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 $205.74   9.490%   $225.2647   $225.26   $225.25   $225.30  
  Purchase #2 $168.50   8.419%   $182.686   $182.69   $182.70   $182.70  
  Purchase #3 $75.51   12.576%   $85.0061   $85.01   $85.00   $85.00  
  Purchase #4 $165.49   9.701%   $181.5442   $181.54   $181.55   $181.50  
  Purchase #5 $183.26   10.107%   $201.7821   $201.78   $201.80   $201.80  
  Purchase #6 $66.41   3.281%   $68.5889   $68.59   $68.60   $68.60  
  Purchase #7 $82.40   10.765%   $91.2704   $91.27   $91.25   $91.30  
  7 purchase totals = $947.31       $1,036.1424   $1,036.14   $1,036.15   $1,036.20