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 $212.55   13.389%   $241.0083   $241.01   $241.00   $241.00  
  Purchase #2 $232.57   8.316%   $251.9105   $251.91   $251.90   $251.90  
  Purchase #3 $96.77   9.658%   $106.116   $106.12   $106.10   $106.10  
  Purchase #4 $201.49   13.204%   $228.0947   $228.09   $228.10   $228.10  
  Purchase #5 $169.55   6.683%   $180.881   $180.88   $180.90   $180.90  
  Purchase #6 $231.29   9.668%   $253.6511   $253.65   $253.65   $253.70  
  Purchase #7 $77.34   10.335%   $85.3331   $85.33   $85.35   $85.30  
  7 purchase totals = $1,221.56       $1,346.9947   $1,346.99   $1,347.00   $1,347.00