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 $58.43   4.836%   $61.2557   $61.26   $61.25   $61.30  
  Purchase #2 $213.32   12.585%   $240.1663   $240.17   $240.15   $240.20  
  Purchase #3 $82.92   13.524%   $94.1341   $94.13   $94.15   $94.10  
  Purchase #4 $101.67   8.707%   $110.5224   $110.52   $110.50   $110.50  
  Purchase #5 $39.29   4.513%   $41.0632   $41.06   $41.05   $41.10  
  Purchase #6 $82.94   9.372%   $90.7131   $90.71   $90.70   $90.70  
  Purchase #7 $194.54   3.823%   $201.9773   $201.98   $202.00   $202.00  
  7 purchase totals = $773.11       $839.8321   $839.83   $839.80   $839.90