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 $96.95   9.780%   $106.4317   $106.43   $106.45   $106.40  
  Purchase #2 $239.81   4.692%   $251.0619   $251.06   $251.05   $251.10  
  Purchase #3 $75.48   4.107%   $78.58   $78.58   $78.60   $78.60  
  Purchase #4 $118.59   4.514%   $123.9432   $123.94   $123.95   $123.90  
  Purchase #5 $209.99   12.242%   $235.697   $235.70   $235.70   $235.70  
  Purchase #6 $11.57   13.345%   $13.114   $13.11   $13.10   $13.10  
  Purchase #7 $241.41   9.256%   $263.7549   $263.75   $263.75   $263.80  
  7 purchase totals = $993.80       $1,072.5827   $1,072.57   $1,072.60   $1,072.60