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 $68.82   6.413%   $73.2334   $73.23   $73.25   $73.20  
  Purchase #2 $181.45   6.724%   $193.6507   $193.65   $193.65   $193.70  
  Purchase #3 $213.87   6.410%   $227.5791   $227.58   $227.60   $227.60  
  Purchase #4 $120.84   8.636%   $131.2757   $131.28   $131.30   $131.30  
  Purchase #5 $234.43   4.273%   $244.4472   $244.45   $244.45   $244.40  
  Purchase #6 $84.25   8.532%   $91.4382   $91.44   $91.45   $91.40  
  Purchase #7 $150.29   12.564%   $169.1724   $169.17   $169.15   $169.20  
  7 purchase totals = $1,053.95       $1,130.7967   $1,130.80   $1,130.85   $1,130.80