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 $213.67   12.819%   $241.0604   $241.06   $241.05   $241.10  
  Purchase #2 $50.84   8.640%   $55.2326   $55.23   $55.25   $55.20  
  Purchase #3 $225.95   3.709%   $234.3305   $234.33   $234.35   $234.30  
  Purchase #4 $43.26   13.278%   $49.0041   $49.00   $49.00   $49.00  
  Purchase #5 $246.91   4.871%   $258.937   $258.94   $258.95   $258.90  
  Purchase #6 $240.97   11.849%   $269.5225   $269.52   $269.50   $269.50  
  Purchase #7 $44.65   10.854%   $49.4963   $49.50   $49.50   $49.50  
  7 purchase totals = $1,066.25       $1,157.5834   $1,157.58   $1,157.60   $1,157.50