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 $243.77   8.356%   $264.1394   $264.14   $264.15   $264.10  
  Purchase #2 $22.27   8.332%   $24.1255   $24.13   $24.15   $24.10  
  Purchase #3 $139.35   7.136%   $149.294   $149.29   $149.30   $149.30  
  Purchase #4 $21.28   11.181%   $23.6593   $23.66   $23.65   $23.70  
  Purchase #5 $218.48   9.172%   $238.519   $238.52   $238.50   $238.50  
  Purchase #6 $171.72   12.633%   $193.4134   $193.41   $193.40   $193.40  
  Purchase #7 $215.50   10.645%   $238.44   $238.44   $238.45   $238.40  
  7 purchase totals = $1,032.37       $1,131.5906   $1,131.59   $1,131.60   $1,131.50