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 $46.77   8.396%   $50.6968   $50.70   $50.70   $50.70  
  Purchase #2 $230.72   11.533%   $257.3289   $257.33   $257.35   $257.30  
  Purchase #3 $29.77   10.771%   $32.9765   $32.98   $33.00   $33.00  
  Purchase #4 $157.98   10.865%   $175.1445   $175.14   $175.15   $175.10  
  Purchase #5 $225.76   7.566%   $242.841   $242.84   $242.85   $242.80  
  Purchase #6 $163.52   13.785%   $186.0612   $186.06   $186.05   $186.10  
  Purchase #7 $232.36   3.536%   $240.5762   $240.58   $240.60   $240.60  
  7 purchase totals = $1,086.88       $1,185.6251   $1,185.63   $1,185.70   $1,185.60