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 $216.98   8.466%   $235.3495   $235.35   $235.35   $235.30  
  Purchase #2 $185.42   11.224%   $206.2315   $206.23   $206.25   $206.20  
  Purchase #3 $46.86   12.718%   $52.8197   $52.82   $52.80   $52.80  
  Purchase #4 $95.26   13.619%   $108.2335   $108.23   $108.25   $108.20  
  Purchase #5 $223.50   9.758%   $245.3091   $245.31   $245.30   $245.30  
  Purchase #6 $80.31   10.759%   $88.9506   $88.95   $88.95   $89.00  
  Purchase #7 $201.61   10.570%   $222.9202   $222.92   $222.90   $222.90  
  7 purchase totals = $1,049.94       $1,159.8141   $1,159.81   $1,159.80   $1,159.70