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 $150.52   8.306%   $163.0222   $163.02   $163.00   $163.00  
  Purchase #2 $205.58   13.293%   $232.9077   $232.91   $232.90   $232.90  
  Purchase #3 $144.42   4.874%   $151.459   $151.46   $151.45   $151.50  
  Purchase #4 $138.99   6.400%   $147.8854   $147.89   $147.90   $147.90  
  Purchase #5 $203.69   3.258%   $210.3262   $210.33   $210.35   $210.30  
  Purchase #6 $123.54   13.771%   $140.5527   $140.55   $140.55   $140.60  
  Purchase #7 $54.25   5.690%   $57.3368   $57.34   $57.35   $57.30  
  7 purchase totals = $1,020.99       $1,103.4900   $1,103.50   $1,103.50   $1,103.50