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 $60.99   13.610%   $69.2907   $69.29   $69.30   $69.30  
  Purchase #2 $152.69   9.268%   $166.8413   $166.84   $166.85   $166.80  
  Purchase #3 $116.52   4.448%   $121.7028   $121.70   $121.70   $121.70  
  Purchase #4 $93.78   9.286%   $102.4884   $102.49   $102.50   $102.50  
  Purchase #5 $181.72   6.838%   $194.146   $194.15   $194.15   $194.10  
  Purchase #6 $189.84   8.605%   $206.1757   $206.18   $206.20   $206.20  
  Purchase #7 $219.94   8.761%   $239.2089   $239.21   $239.20   $239.20  
  7 purchase totals = $1,015.48       $1,099.8538   $1,099.86   $1,099.90   $1,099.80