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 $125.49   13.670%   $142.6445   $142.64   $142.65   $142.60  
  Purchase #2 $211.75   11.759%   $236.6497   $236.65   $236.65   $236.60  
  Purchase #3 $27.51   6.112%   $29.1914   $29.19   $29.20   $29.20  
  Purchase #4 $166.72   3.313%   $172.2434   $172.24   $172.25   $172.20  
  Purchase #5 $77.79   10.295%   $85.7985   $85.80   $85.80   $85.80  
  Purchase #6 $206.63   6.310%   $219.6684   $219.67   $219.65   $219.70  
  Purchase #7 $163.92   13.494%   $186.0394   $186.04   $186.05   $186.00  
  7 purchase totals = $979.81       $1,072.2353   $1,072.23   $1,072.25   $1,072.10