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 $52.81   7.168%   $56.5954   $56.60   $56.60   $56.60  
  Purchase #2 $94.31   10.645%   $104.3493   $104.35   $104.35   $104.30  
  Purchase #3 $99.51   6.804%   $106.2807   $106.28   $106.30   $106.30  
  Purchase #4 $203.99   10.693%   $225.8027   $225.80   $225.80   $225.80  
  Purchase #5 $124.93   7.256%   $133.9949   $133.99   $134.00   $134.00  
  Purchase #6 $246.54   12.582%   $277.5597   $277.56   $277.55   $277.60  
  Purchase #7 $218.26   9.583%   $239.1759   $239.18   $239.20   $239.20  
  7 purchase totals = $1,040.35       $1,143.7586   $1,143.76   $1,143.80   $1,143.80