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 $94.43   9.809%   $103.6926   $103.69   $103.70   $103.70  
  Purchase #2 $207.65   9.724%   $227.8419   $227.84   $227.85   $227.80  
  Purchase #3 $239.91   5.178%   $252.3325   $252.33   $252.35   $252.30  
  Purchase #4 $67.41   12.651%   $75.938   $75.94   $75.95   $75.90  
  Purchase #5 $209.69   12.733%   $236.3898   $236.39   $236.40   $236.40  
  Purchase #6 $84.67   10.644%   $93.6823   $93.68   $93.70   $93.70  
  Purchase #7 $57.91   13.393%   $65.6659   $65.67   $65.65   $65.70  
  7 purchase totals = $961.67       $1,055.5430   $1,055.54   $1,055.60   $1,055.50