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 $49.29   5.596%   $52.0483   $52.05   $52.05   $52.00  
  Purchase #2 $234.62   10.827%   $260.0223   $260.02   $260.00   $260.00  
  Purchase #3 $56.64   11.356%   $63.072   $63.07   $63.05   $63.10  
  Purchase #4 $45.95   13.267%   $52.0462   $52.05   $52.05   $52.00  
  Purchase #5 $27.82   4.575%   $29.0928   $29.09   $29.10   $29.10  
  Purchase #6 $245.29   7.122%   $262.7596   $262.76   $262.75   $262.80  
  Purchase #7 $49.59   10.157%   $54.6269   $54.63   $54.65   $54.60  
  7 purchase totals = $709.20       $773.6681   $773.67   $773.65   $773.60