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 $182.26   13.171%   $206.2655   $206.27   $206.25   $206.30  
  Purchase #2 $200.32   11.731%   $223.8195   $223.82   $223.80   $223.80  
  Purchase #3 $211.89   3.258%   $218.7934   $218.79   $218.80   $218.80  
  Purchase #4 $231.58   13.506%   $262.8572   $262.86   $262.85   $262.90  
  Purchase #5 $234.52   12.234%   $263.2112   $263.21   $263.20   $263.20  
  Purchase #6 $197.77   5.866%   $209.3712   $209.37   $209.35   $209.40  
  Purchase #7 $39.30   8.593%   $42.677   $42.68   $42.70   $42.70  
  7 purchase totals = $1,297.64       $1,426.9950   $1,427.00   $1,426.95   $1,427.10