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 $84.94   12.656%   $95.69   $95.69   $95.70   $95.70  
  Purchase #2 $123.48   3.274%   $127.5227   $127.52   $127.50   $127.50  
  Purchase #3 $137.25   13.706%   $156.0615   $156.06   $156.05   $156.10  
  Purchase #4 $242.98   10.753%   $269.1076   $269.11   $269.10   $269.10  
  Purchase #5 $235.68   4.450%   $246.1678   $246.17   $246.15   $246.20  
  Purchase #6 $80.53   4.652%   $84.2763   $84.28   $84.30   $84.30  
  Purchase #7 $229.74   13.329%   $260.362   $260.36   $260.35   $260.40  
  7 purchase totals = $1,134.60       $1,239.1879   $1,239.19   $1,239.15   $1,239.30