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 $198.54   3.215%   $204.9231   $204.92   $204.90   $204.90  
  Purchase #2 $218.99   7.587%   $235.6048   $235.60   $235.60   $235.60  
  Purchase #3 $54.94   10.258%   $60.5757   $60.58   $60.60   $60.60  
  Purchase #4 $91.78   11.245%   $102.1007   $102.10   $102.10   $102.10  
  Purchase #5 $5.77   8.467%   $6.2585   $6.26   $6.25   $6.30  
  Purchase #6 $162.37   6.119%   $172.3054   $172.31   $172.30   $172.30  
  Purchase #7 $13.74   3.787%   $14.2603   $14.26   $14.25   $14.30  
  7 purchase totals = $746.13       $796.0285   $796.03   $796.00   $796.10