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 $57.35   12.645%   $64.6019   $64.60   $64.60   $64.60  
  Purchase #2 $189.31   6.209%   $201.0643   $201.06   $201.05   $201.10  
  Purchase #3 $22.39   11.650%   $24.9984   $25.00   $25.00   $25.00  
  Purchase #4 $210.85   13.713%   $239.7639   $239.76   $239.75   $239.80  
  Purchase #5 $73.91   12.241%   $82.9573   $82.96   $82.95   $83.00  
  Purchase #6 $72.35   3.753%   $75.0653   $75.07   $75.05   $75.10  
  Purchase #7 $190.62   13.477%   $216.3099   $216.31   $216.30   $216.30  
  7 purchase totals = $816.78       $904.7610   $904.76   $904.70   $904.90