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 $61.65   12.643%   $69.4444   $69.44   $69.45   $69.40  
  Purchase #2 $58.79   11.874%   $65.7707   $65.77   $65.75   $65.80  
  Purchase #3 $29.58   7.343%   $31.7521   $31.75   $31.75   $31.80  
  Purchase #4 $115.61   11.658%   $129.0878   $129.09   $129.10   $129.10  
  Purchase #5 $180.31   6.785%   $192.544   $192.54   $192.55   $192.50  
  Purchase #6 $52.95   12.457%   $59.546   $59.55   $59.55   $59.50  
  Purchase #7 $121.49   4.393%   $126.8271   $126.83   $126.85   $126.80  
  7 purchase totals = $620.38       $674.9721   $674.97   $675.00   $674.90