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 $236.51   8.746%   $257.1952   $257.20   $257.20   $257.20  
  Purchase #2 $24.46   11.216%   $27.2034   $27.20   $27.20   $27.20  
  Purchase #3 $119.45   10.169%   $131.5969   $131.60   $131.60   $131.60  
  Purchase #4 $131.58   12.165%   $147.5867   $147.59   $147.60   $147.60  
  Purchase #5 $216.91   13.767%   $246.772   $246.77   $246.75   $246.80  
  Purchase #6 $200.85   5.780%   $212.4591   $212.46   $212.45   $212.50  
  Purchase #7 $172.96   4.619%   $180.949   $180.95   $180.95   $180.90  
  7 purchase totals = $1,102.72       $1,203.7623   $1,203.77   $1,203.75   $1,203.80