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 $142.85   13.413%   $162.0105   $162.01   $162.00   $162.00  
  Purchase #2 $86.94   11.122%   $96.6095   $96.61   $96.60   $96.60  
  Purchase #3 $78.97   11.463%   $88.0223   $88.02   $88.00   $88.00  
  Purchase #4 $140.80   5.438%   $148.4567   $148.46   $148.45   $148.50  
  Purchase #5 $153.82   10.573%   $170.0834   $170.08   $170.10   $170.10  
  Purchase #6 $177.49   3.551%   $183.7927   $183.79   $183.80   $183.80  
  Purchase #7 $237.94   6.862%   $254.2674   $254.27   $254.25   $254.30  
  7 purchase totals = $1,018.81       $1,103.2425   $1,103.24   $1,103.20   $1,103.30