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 $84.57   7.864%   $91.2206   $91.22   $91.20   $91.20  
  Purchase #2 $136.27   8.292%   $147.5695   $147.57   $147.55   $147.60  
  Purchase #3 $164.42   8.202%   $177.9057   $177.91   $177.90   $177.90  
  Purchase #4 $209.88   9.859%   $230.5721   $230.57   $230.55   $230.60  
  Purchase #5 $241.65   6.731%   $257.9155   $257.92   $257.90   $257.90  
  Purchase #6 $54.81   4.502%   $57.2775   $57.28   $57.30   $57.30  
  Purchase #7 $47.49   9.449%   $51.9773   $51.98   $52.00   $52.00  
  7 purchase totals = $939.09       $1,014.4382   $1,014.45   $1,014.40   $1,014.50