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 $97.36   13.300%   $110.3089   $110.31   $110.30   $110.30  
  Purchase #2 $167.94   6.559%   $178.9552   $178.96   $178.95   $179.00  
  Purchase #3 $235.59   7.148%   $252.43   $252.43   $252.45   $252.40  
  Purchase #4 $178.32   4.745%   $186.7813   $186.78   $186.80   $186.80  
  Purchase #5 $14.36   11.754%   $16.0479   $16.05   $16.05   $16.00  
  Purchase #6 $206.82   3.404%   $213.8602   $213.86   $213.85   $213.90  
  Purchase #7 $94.78   6.737%   $101.1653   $101.17   $101.15   $101.20  
  7 purchase totals = $995.17       $1,059.5488   $1,059.56   $1,059.55   $1,059.60