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 $163.62   10.804%   $181.2975   $181.30   $181.30   $181.30  
  Purchase #2 $55.88   12.140%   $62.6638   $62.66   $62.65   $62.70  
  Purchase #3 $15.68   7.764%   $16.8974   $16.90   $16.90   $16.90  
  Purchase #4 $167.99   4.259%   $175.1447   $175.14   $175.15   $175.10  
  Purchase #5 $150.54   4.447%   $157.2345   $157.23   $157.25   $157.20  
  Purchase #6 $51.82   10.197%   $57.1041   $57.10   $57.10   $57.10  
  Purchase #7 $201.73   11.652%   $225.2356   $225.24   $225.25   $225.20  
  7 purchase totals = $807.26       $875.5776   $875.57   $875.60   $875.50