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 $246.73   11.269%   $274.534   $274.53   $274.55   $274.50  
  Purchase #2 $172.95   6.264%   $183.7836   $183.78   $183.80   $183.80  
  Purchase #3 $46.84   11.566%   $52.2575   $52.26   $52.25   $52.30  
  Purchase #4 $232.75   3.537%   $240.9824   $240.98   $241.00   $241.00  
  Purchase #5 $65.75   12.566%   $74.0121   $74.01   $74.00   $74.00  
  Purchase #6 $86.79   3.787%   $90.0767   $90.08   $90.10   $90.10  
  Purchase #7 $86.33   11.267%   $96.0568   $96.06   $96.05   $96.10  
  7 purchase totals = $938.14       $1,011.7031   $1,011.70   $1,011.75   $1,011.80