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 $234.49   7.868%   $252.9397   $252.94   $252.95   $252.90  
  Purchase #2 $167.35   5.574%   $176.6781   $176.68   $176.70   $176.70  
  Purchase #3 $225.55   6.121%   $239.3559   $239.36   $239.35   $239.40  
  Purchase #4 $221.50   4.104%   $230.5904   $230.59   $230.60   $230.60  
  Purchase #5 $64.56   11.381%   $71.9076   $71.91   $71.90   $71.90  
  Purchase #6 $247.26   11.638%   $276.0361   $276.04   $276.05   $276.00  
  Purchase #7 $68.59   9.302%   $74.9702   $74.97   $74.95   $75.00  
  7 purchase totals = $1,229.30       $1,322.4780   $1,322.49   $1,322.50   $1,322.50