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 $232.35   13.553%   $263.8404   $263.84   $263.85   $263.80  
  Purchase #2 $68.25   6.786%   $72.8814   $72.88   $72.90   $72.90  
  Purchase #3 $90.65   12.472%   $101.9559   $101.96   $101.95   $102.00  
  Purchase #4 $203.99   3.548%   $211.2276   $211.23   $211.25   $211.20  
  Purchase #5 $67.56   8.522%   $73.3175   $73.32   $73.30   $73.30  
  Purchase #6 $151.66   3.301%   $156.6663   $156.67   $156.65   $156.70  
  Purchase #7 $159.49   13.415%   $180.8856   $180.89   $180.90   $180.90  
  7 purchase totals = $973.95       $1,060.7747   $1,060.79   $1,060.80   $1,060.80