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 $185.98   8.351%   $201.5112   $201.51   $201.50   $201.50  
  Purchase #2 $24.32   7.619%   $26.1729   $26.17   $26.15   $26.20  
  Purchase #3 $73.94   11.179%   $82.2058   $82.21   $82.20   $82.20  
  Purchase #4 $215.93   12.297%   $242.4829   $242.48   $242.50   $242.50  
  Purchase #5 $170.54   3.487%   $176.4867   $176.49   $176.50   $176.50  
  Purchase #6 $182.59   13.310%   $206.8927   $206.89   $206.90   $206.90  
  Purchase #7 $141.55   10.835%   $156.8869   $156.89   $156.90   $156.90  
  7 purchase totals = $994.85       $1,092.6391   $1,092.64   $1,092.65   $1,092.70