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 $69.65   5.231%   $73.2934   $73.29   $73.30   $73.30  
  Purchase #2 $119.72   11.344%   $133.301   $133.30   $133.30   $133.30  
  Purchase #3 $5.56   9.629%   $6.0954   $6.10   $6.10   $6.10  
  Purchase #4 $135.92   9.849%   $149.3068   $149.31   $149.30   $149.30  
  Purchase #5 $134.37   5.259%   $141.4365   $141.44   $141.45   $141.40  
  Purchase #6 $120.40   5.171%   $126.6259   $126.63   $126.65   $126.60  
  Purchase #7 $173.26   13.132%   $196.0125   $196.01   $196.00   $196.00  
  7 purchase totals = $758.88       $826.0715   $826.08   $826.10   $826.00