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 $143.92   10.781%   $159.436   $159.44   $159.45   $159.40  
  Purchase #2 $102.47   8.279%   $110.9535   $110.95   $110.95   $111.00  
  Purchase #3 $88.52   10.509%   $97.8226   $97.82   $97.80   $97.80  
  Purchase #4 $218.99   7.173%   $234.6982   $234.70   $234.70   $234.70  
  Purchase #5 $102.77   6.124%   $109.0636   $109.06   $109.05   $109.10  
  Purchase #6 $216.26   7.423%   $232.313   $232.31   $232.30   $232.30  
  Purchase #7 $48.33   8.566%   $52.4699   $52.47   $52.45   $52.50  
  7 purchase totals = $921.26       $996.7568   $996.75   $996.70   $996.80