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 $191.86   5.264%   $201.9595   $201.96   $201.95   $202.00  
  Purchase #2 $24.57   4.536%   $25.6845   $25.68   $25.70   $25.70  
  Purchase #3 $87.69   3.833%   $91.0512   $91.05   $91.05   $91.10  
  Purchase #4 $65.44   12.717%   $73.762   $73.76   $73.75   $73.80  
  Purchase #5 $57.93   13.364%   $65.6718   $65.67   $65.65   $65.70  
  Purchase #6 $244.54   10.371%   $269.9012   $269.90   $269.90   $269.90  
  Purchase #7 $66.67   12.760%   $75.1771   $75.18   $75.20   $75.20  
  7 purchase totals = $738.70       $803.2073   $803.20   $803.20   $803.40