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 $62.92   11.399%   $70.0923   $70.09   $70.10   $70.10  
  Purchase #2 $177.91   12.306%   $199.8036   $199.80   $199.80   $199.80  
  Purchase #3 $68.55   6.356%   $72.907   $72.91   $72.90   $72.90  
  Purchase #4 $74.29   4.373%   $77.5387   $77.54   $77.55   $77.50  
  Purchase #5 $209.69   6.803%   $223.9552   $223.96   $223.95   $224.00  
  Purchase #6 $22.71   13.395%   $25.752   $25.75   $25.75   $25.80  
  Purchase #7 $194.45   12.736%   $219.2152   $219.22   $219.20   $219.20  
  7 purchase totals = $810.52       $889.2640   $889.27   $889.25   $889.30