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 $238.48   11.833%   $266.6993   $266.70   $266.70   $266.70  
  Purchase #2 $243.69   3.310%   $251.7561   $251.76   $251.75   $251.80  
  Purchase #3 $84.62   12.308%   $95.035   $95.04   $95.05   $95.00  
  Purchase #4 $60.30   7.681%   $64.9316   $64.93   $64.95   $64.90  
  Purchase #5 $34.57   11.270%   $38.466   $38.47   $38.45   $38.50  
  Purchase #6 $23.52   8.460%   $25.5098   $25.51   $25.50   $25.50  
  Purchase #7 $149.30   8.630%   $162.1846   $162.18   $162.20   $162.20  
  7 purchase totals = $834.48       $904.5824   $904.59   $904.60   $904.60