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 $207.82   13.209%   $235.2709   $235.27   $235.25   $235.30  
  Purchase #2 $66.60   4.641%   $69.6909   $69.69   $69.70   $69.70  
  Purchase #3 $207.79   13.671%   $236.197   $236.20   $236.20   $236.20  
  Purchase #4 $29.97   11.213%   $33.3305   $33.33   $33.35   $33.30  
  Purchase #5 $237.27   12.803%   $267.6477   $267.65   $267.65   $267.60  
  Purchase #6 $47.35   9.760%   $51.9714   $51.97   $51.95   $52.00  
  Purchase #7 $227.31   11.685%   $253.8712   $253.87   $253.85   $253.90  
  7 purchase totals = $1,024.11       $1,147.9796   $1,147.98   $1,147.95   $1,148.00