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 $222.41   5.517%   $234.6804   $234.68   $234.70   $234.70  
  Purchase #2 $52.75   10.495%   $58.2861   $58.29   $58.30   $58.30  
  Purchase #3 $211.73   8.873%   $230.5168   $230.52   $230.50   $230.50  
  Purchase #4 $58.89   9.372%   $64.4092   $64.41   $64.40   $64.40  
  Purchase #5 $98.92   13.145%   $111.923   $111.92   $111.90   $111.90  
  Purchase #6 $216.53   12.312%   $243.1892   $243.19   $243.20   $243.20  
  Purchase #7 $113.81   10.817%   $126.1208   $126.12   $126.10   $126.10  
  7 purchase totals = $975.04       $1,069.1255   $1,069.13   $1,069.10   $1,069.10