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 $179.77   12.797%   $202.7752   $202.78   $202.80   $202.80  
  Purchase #2 $51.78   10.519%   $57.2267   $57.23   $57.25   $57.20  
  Purchase #3 $162.52   13.416%   $184.3237   $184.32   $184.30   $184.30  
  Purchase #4 $21.89   3.380%   $22.6299   $22.63   $22.65   $22.60  
  Purchase #5 $232.25   4.620%   $242.98   $242.98   $243.00   $243.00  
  Purchase #6 $32.64   13.415%   $37.0187   $37.02   $37.00   $37.00  
  Purchase #7 $98.49   7.295%   $105.6748   $105.67   $105.65   $105.70  
  7 purchase totals = $779.34       $852.6290   $852.63   $852.65   $852.60