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 $83.64   12.153%   $93.8048   $93.80   $93.80   $93.80  
  Purchase #2 $45.26   3.276%   $46.7427   $46.74   $46.75   $46.70  
  Purchase #3 $106.41   11.342%   $118.479   $118.48   $118.50   $118.50  
  Purchase #4 $183.56   9.653%   $201.279   $201.28   $201.30   $201.30  
  Purchase #5 $105.40   11.384%   $117.3987   $117.40   $117.40   $117.40  
  Purchase #6 $86.62   13.833%   $98.6021   $98.60   $98.60   $98.60  
  Purchase #7 $17.52   12.202%   $19.6578   $19.66   $19.65   $19.70  
  7 purchase totals = $628.41       $695.9641   $695.96   $696.00   $696.00